diff --git a/airdef-mod/NOTES-terrain-guidance.md b/airdef-mod/NOTES-terrain-guidance.md
new file mode 100644
index 0000000..a72f186
--- /dev/null
+++ b/airdef-mod/NOTES-terrain-guidance.md
@@ -0,0 +1,5 @@
+Status of terrain-aware flight (not committed):
+- Done: sim/terrain.rs (look-ahead terrain following, dive only down a clear line, interceptor steer/loft/self-destruct, launch predicate), planner relief pricing + spawn above land (raid.rs), SAM launch check + why line (mod.rs, why.rs), Tally.scrubbed, world.probe, harness terrain fixes, 6 new tests in regress.rs. Build has no warnings; cargo test passes (43 + 4).
+- Numbers (6 seeds, sim_run big-smart): hills:70:100:140 crashes 13 -> 3, hills:70:150:120 29 -> 2, default hills 2 -> 2 (all terminal-dive near-target by Kh101/Kalibr).
+- Half-done / known: terminal dive of slow-turning cruise missiles still sometimes hits ground 7-20 blocks short of target; hills:70:150:120 tick max 38 ms / p95 2 ms (planner terrain phase + ground queries) not profiled; not tested in game.
+- Next: tune dive geometry for Kh101/Kalibr, profile the planner's 1024-columns-per-tick height requests, optional in-game check.
diff --git a/airdef-mod/examples/sim_run/harness.rs b/airdef-mod/examples/sim_run/harness.rs
index 41d7de4..e6c4c01 100644
--- a/airdef-mod/examples/sim_run/harness.rs
+++ b/airdef-mod/examples/sim_run/harness.rs
@@ -108,6 +108,8 @@ pub struct Report {
     /// The block cache's counters (issue #43) and the drones that struck the land (issue #42).
     pub world: String,
     pub crashes: u32,
+    /// What went wrong for the air defence, as the raid report words it.
+    pub failures: String,
     pub ground_batches: u64,
     pub tick_p50: Duration,
     pub tick_p95: Duration,
@@ -135,14 +137,16 @@ pub fn run(sc: &Scenario) -> Report {
     sim.damage = false; // explosions would change the land the height function describes
     for u in &sc.units {
         let id = sim.id();
-        let mut s = Sam::new(id, u.kind, u.pos, u.heading);
+        // Systems stand on the land, whatever the layout says.
+        let pos = DVec3::new(u.pos.x, f64::from(sc.terrain.height(u.pos.x.floor() as i32, u.pos.z.floor() as i32)), u.pos.z);
+        let mut s = Sam::new(id, u.kind, pos, u.heading);
         if u.empty {
             s.empty = true;
             s.missiles = 0;
         }
         sim.sams.push(s);
     }
-    sim.targets = sc.objects.clone();
+    sim.targets = sc.objects.iter().map(|o| DVec3::new(o.x, f64::from(sc.terrain.height(o.x.floor() as i32, o.z.floor() as i32)), o.z)).collect();
     sim.target_health = vec![100.0; sc.objects.len()];
     if sc.ew {
         sim.set_ew(true);
@@ -163,7 +167,8 @@ pub fn run(sc: &Scenario) -> Report {
             if !ordered[i] && now >= spec.at && !sim.planning() && (i == 0 || ended[i - 1]) {
                 let order = RaidOrder { kinds: spec.kinds.clone(), approach: spec.approach, dist: spec.dist, aim: spec.aim };
                 launched_before[i] = sim.launched;
-                sim.order_raid(&order, &sc.objects, &mut out);
+                let objects = sim.targets.clone();
+                sim.order_raid(&order, &objects, &mut out);
                 ordered[i] = true;
             }
         }
@@ -226,6 +231,7 @@ pub fn run(sc: &Scenario) -> Report {
     r.raids_ordered = ordered.iter().filter(|o| **o).count();
     r.world = ground.world.text();
     r.crashes = sim.crashes;
+    r.failures = sim.tally.text();
     r.raids_ended = ended.iter().filter(|o| **o).count();
     r.all_ended = r.raids_ended == sc.raids.len();
     r.tick_total = times.iter().sum();
@@ -268,7 +274,8 @@ impl Report {
              ground queries: {gq} in {gb} batches\n\
              non-finite positions: {nan}\n\
              stuck trucks: {stuck:?} (busy truck-ticks {busy})\n\
-             crashes into the land: {crashes}; {world}\n",
+             crashes into the land: {crashes}; {world}\n\
+             air-defence failures: {failures}\n",
             name = self.name,
             seed = self.seed,
             units = self.units,
@@ -293,6 +300,7 @@ impl Report {
             busy = self.truck_busy_ticks,
             crashes = self.crashes,
             world = self.world,
+            failures = if self.failures.is_empty() { "none" } else { &self.failures },
         )
     }
     pub fn json(&self) -> String {
diff --git a/airdef-mod/src/sim/mod.rs b/airdef-mod/src/sim/mod.rs
index fd92837..25d7430 100644
--- a/airdef-mod/src/sim/mod.rs
+++ b/airdef-mod/src/sim/mod.rs
@@ -14,6 +14,7 @@ pub mod fires;
 mod raid;
 pub mod record;
 mod sight;
+mod terrain;
 mod ew;
 mod lights;
 mod logistics;
@@ -745,6 +746,23 @@ pub struct Drone {
     sector: u8,
     /// Sent by the smart enemy: it may be turned on systems that give themselves away.
     smart: bool,
+    /// What the land ahead asks of its flight (see `terrain`).
+    nav: Nav,
+}
+
+/// A drone's terrain following: refreshed every few ticks, used every one.
+#[derive(Clone, Copy, Debug)]
+struct Nav {
+    /// The height it must be at now to clear the land ahead (unknown: -inf).
+    need: f64,
+    /// The height from which a straight dive on its target clears the land (unknown: -inf).
+    dive: f64,
+}
+
+impl Default for Nav {
+    fn default() -> Self {
+        Nav { need: f64::NEG_INFINITY, dive: f64::NEG_INFINITY }
+    }
 }
 
 impl Drone {
@@ -1073,6 +1091,10 @@ pub struct Sam {
     pub ew_lock: bool,
     /// Ticks till a gun fires its next illumination flare.
     flare_cd: u32,
+    /// Shots the land ruled out, by target: when it was judged and why (`terrain::MASKED`, `terrain::PATH_BLOCKED`).
+    pub(super) terrain: HashMap<u32, (u64, u8)>,
+    /// Targets whose land hasn't been answered yet, and since when it has been waited for.
+    waits: HashMap<u32, u64>,
 }
 
 impl Sam {
@@ -1124,6 +1146,8 @@ impl Sam {
             heat: 0.0,
             ew_lock: false,
             flare_cd: 0,
+            terrain: HashMap::new(),
+            waits: HashMap::new(),
         }
     }
     pub fn alive(&self) -> bool {
@@ -1384,6 +1408,7 @@ impl Sim {
             jammed: false,
             sector: 0,
             smart: false,
+            nav: Nav::default(),
         });
         self.launched += 1;
     }
@@ -1433,7 +1458,7 @@ impl Sim {
     /// One game tick.
     pub fn step(&mut self, ground: &mut Ground, player: Option<DVec3>, out: &mut Out) {
         self.tick += 1;
-        self.plan_step(out);
+        self.plan_step(Some(&mut *ground), out);
         self.adapt();
         self.release_queue();
         self.step_drones(ground, player, out);
@@ -1443,7 +1468,7 @@ impl Sim {
         self.step_ew(out);
         self.update_sight(ground);
         self.step_lights(out);
-        self.step_sams(out);
+        self.step_sams(ground, out);
         self.step_missiles(ground, out);
         self.step_fx(ground, out);
         self.draw_targets(out);
@@ -1473,7 +1498,7 @@ impl Sim {
             let spec = d.kind.spec();
             let below = ground.at(d.pos, now);
             let from = d.pos;
-            ground.ahead(d.pos, d.vel, 20.0, now);
+            ground.ahead(d.pos, d.vel, (120.0 / d.vel.length().max(0.05)).max(20.0), now);
             // Near its aim it looks at the land there again: a platform or hilltop blown away
             // meanwhile, it goes for what is left below, not for the air where it stood.
             if d.flight != Flight::Falling
@@ -1596,9 +1621,6 @@ impl Sim {
                 }
                 continue;
             }
-            if d.flight == Flight::Cruise && d.route.len() <= 1 && horizontal(d.target - d.pos).length() < spec.dive {
-                d.flight = Flight::Dive;
-            }
             // An interceptor coming: drones drop to the treetops (radars lose them sooner).
             if d.engaged > 0 && matches!(spec.class, Class::Drone | Class::Jet) {
                 d.low = true;
@@ -1614,24 +1636,86 @@ impl Sim {
             {
                 d.route.remove(0);
             }
-            let goal = if d.flight == Flight::Dive {
-                d.target
-            } else {
-                // Cruise height over the target, and `clearance` over the land ahead.
-                let ahead = ground.at(d.pos + horizontal(d.vel).normalize_or_zero() * 20.0, now);
-                let floor = match (below, ahead) {
-                    (Some(a), Some(b)) => a.max(b) + spec.clearance,
-                    (Some(g), None) | (None, Some(g)) => g + spec.clearance,
-                    (None, None) => d.target.y + spec.clearance,
-                };
-                let to = d.route.first().copied().unwrap_or(d.target);
-                // Under the radars: as low as the land lets it, all the way.
-                let height = if d.low { floor.max(d.target.y + 4.0) } else { (d.target.y + spec.cruise).max(floor) };
-                DVec3::new(to.x, height, to.z)
+            let climb = d.kind.climb();
+            // A dive begins far enough out to bring it down onto the target: a missile that turns slowly needs a long
+            // way to lose height it has over the aim.
+            let dive_at = {
+                let r = spec.speed * 1.35 / (spec.turn * 3.5).max(0.01);
+                let drop = (d.pos.y - d.target.y).clamp(0.0, r);
+                spec.dive.max(((2.0 * r * drop - drop * drop).sqrt() * 1.1).min(spec.dive * 2.5))
             };
+            let way = d.route.first().copied().unwrap_or(d.target);
+            let to_target = horizontal(d.target - d.pos).length();
+            // What the land ahead asks: along its heading and towards its next point, several seconds out.
+            if d.age <= 1 || (now + u64::from(d.id)) % 3 == 0 {
+                let heading = horizontal(d.vel).normalize_or_zero();
+                let towards = horizontal(way - d.pos).normalize_or_zero();
+                let look = d.kind.look_len();
+                let mut lines = vec![(heading, look)];
+                let angle = heading.angle_between(towards);
+                if towards != DVec3::ZERO && angle > 0.1 {
+                    let reach = look.min(horizontal(way - d.pos).length() + 30.0);
+                    lines.push((towards, reach));
+                    if angle > 0.4 {
+                        lines.push(((heading + towards).normalize_or_zero(), reach));
+                    }
+                }
+                d.nav.need = terrain::required_height(ground, d.pos, &lines, spec.clearance, &climb).unwrap_or(f64::NEG_INFINITY);
+                d.nav.dive = if to_target < dive_at * 3.0 {
+                    terrain::dive_height(ground, d.pos, d.target, terrain::DIVE_MARGIN).unwrap_or(f64::NEG_INFINITY)
+                } else {
+                    f64::NEG_INFINITY
+                };
+            }
+            // The dive into the target starts when the line down to it is clear of the land, else it comes in higher;
+            // a dive that finds the line blocked pulls out and climbs.
+            if d.flight == Flight::Cruise && d.route.len() <= 1 && to_target < dive_at && d.pos.y >= d.nav.dive - 1.0 && d.vel.y < 0.3 * spec.speed {
+                d.flight = Flight::Dive;
+            } else if d.flight == Flight::Dive && to_target > 40.0 && d.pos.y < d.nav.dive - 4.0 {
+                d.flight = Flight::Cruise;
+            }
             let rate = if d.flight == Flight::Dive { spec.turn * 3.5 } else { spec.turn };
             let old = d.vel.normalize_or(DVec3::NEG_Z);
-            let new = turn(old, goal - d.pos, rate);
+            let probe_len = (spec.speed * 10.0).clamp(50.0, 150.0);
+            let new = if d.flight == Flight::Dive {
+                let mut new = turn(old, d.target - d.pos, rate);
+                // Something solid across the dive, short of the target (a building the heights don't show): up and round.
+                if to_target > 40.0
+                    && d.age > 8
+                    && let world::Sweep::Hit { point, .. } = ground.world.probe(d.pos, d.pos + new * probe_len.min(to_target - 20.0), now)
+                    && point.distance(d.target) > 16.0
+                {
+                    d.flight = Flight::Cruise;
+                    d.nav.need = d.nav.need.max(point.y + spec.clearance);
+                    new = turn(old, horizontal(way - d.pos).normalize_or(horizontal(old)) + DVec3::Y * climb.pitch.tan(), spec.turn);
+                }
+                new
+            } else {
+                let heading = horizontal(way - d.pos).normalize_or(horizontal(old).normalize_or(DVec3::NEG_Z));
+                // Cruise height over the target; as low as the land lets it when under the radars.
+                let base = if d.low { d.target.y + 4.0 } else { d.target.y + spec.cruise };
+                let own = below.map_or(f64::NEG_INFINITY, |g| g + spec.clearance);
+                let need = d.nav.need.max(own);
+                let safe = if need.is_finite() { need + 2.0 } else { d.target.y + spec.clearance };
+                let height = base.max(safe).max(d.nav.dive + 1.0);
+                let full = climb.pitch.tan();
+                let urgent = need.is_finite() && d.pos.y < need;
+                let slope = if urgent {
+                    full
+                } else {
+                    ((height - d.pos.y) / (climb.radius * 1.5).min((to_target * 0.5).max(30.0)).max(30.0)).clamp(-0.35, full)
+                };
+                let mut new = terrain::fly_towards(old, heading, slope, rate, urgent);
+                // Something solid ahead that the heights don't show (trees, a building, an overhang): climb.
+                if d.age > 8
+                    && let world::Sweep::Hit { point, .. } =
+                        ground.world.probe(d.pos - DVec3::Y * 4.0, d.pos - DVec3::Y * 4.0 + new * probe_len, now)
+                {
+                    d.nav.need = d.nav.need.max(point.y + spec.clearance);
+                    new = terrain::fly_towards(old, heading, full, rate, true);
+                }
+                terrain::clamp_pitch(new, -0.6, climb.pitch, heading)
+            };
             let side = old.cross(new).y;
             d.roll += ((side * 40.0).clamp(-0.8, 0.8) - d.roll) * 0.15;
             let speed = if d.flight == Flight::Dive { spec.speed * 1.35 } else { spec.speed };
@@ -1733,6 +1817,7 @@ impl Sim {
                 jammed: false,
                 sector,
                 smart: false,
+                nav: Nav::default(),
             });
         }
         for d in &self.drones {
@@ -1884,7 +1969,7 @@ impl Sim {
 
     // ------------------------------------------------ air defence
 
-    fn step_sams(&mut self, out: &mut Out) {
+    fn step_sams(&mut self, ground: &mut Ground, out: &mut Out) {
         if self.hold {
             for i in 0..self.sams.len() {
                 if self.sams[i].alive() && !self.sams[i].moving() {
@@ -1923,6 +2008,11 @@ impl Sim {
                     sam.dish = sam.beam;
                 }
                 sam.jam = sam.jam.saturating_sub(1);
+                if self.tick % 64 == 0 {
+                    let now = self.tick;
+                    sam.terrain.retain(|_, (when, _)| now.saturating_sub(*when) < 4 * terrain::VERDICT_AGE);
+                    sam.waits.retain(|_, since| now.saturating_sub(*since) < 4 * terrain::WAIT_TICKS);
+                }
                 if sam.reloading > 0 {
                     sam.reloading -= 1;
                     if sam.reloading == 0 {
@@ -1950,7 +2040,10 @@ impl Sim {
             let (had_target, had_gun) = (self.sams[i].target, self.sams[i].gun_target);
             let now = self.tick;
             let (target, gun_target) = {
-                let tracks = &self.sams[i].tracks;
+                let me = &self.sams[i];
+                let tracks = &me.tracks;
+                // A shot the land ruled out a moment ago is not tried again at once.
+                let open = |id: u32| me.terrain_verdict(id, now).is_none_or(|b| b == 0);
                 // The conditions are `why`'s, shared with the diagnostic. A system knows its targets by their tracks:
                 // the forecast of the last measurement, never the true place.
                 let drone = |tr: &Track| drone_at.get(&tr.id).map(|&k| &self.drones[k]);
@@ -1958,7 +2051,7 @@ impl Sim {
                 let needed = why::needed;
                 let target = spec.missile.as_ref().map(|load| {
                     let ok = |tr: &Track, k: f64| {
-                        drone(tr).is_some_and(|d| why::allowed(roles, tr, now, d) && why::in_reach(load.min, load.max, k, pos, tr.est(now)))
+                        drone(tr).is_some_and(|d| why::allowed(roles, tr, now, d) && open(tr.id) && why::in_reach(load.min, load.max, k, pos, tr.est(now)))
                     };
                     let keep = had_target.filter(|t| tracks.iter().any(|tr| tr.id == *t && ok(tr, 1.1)));
                     keep.or_else(|| {
@@ -2133,9 +2226,38 @@ impl Sim {
                 // The missile turns after its boost, but the launcher must point near the target.
                 let t = sam.track(mt).filter(|_| drone_at.contains_key(&mt)).map(|tr| tr.est(now));
                 let aligned = why::missile_aligned(spec.family, sam.yaw, mount, t, aim_id, mt, aim_error);
-                if ready && aligned {
-                    let n = load.magazine - sam.missiles;
-                    let (muzzle, dir) = sam.muzzle(n);
+                let n = load.magazine - sam.missiles;
+                let (muzzle, dir) = sam.muzzle(n);
+                // The land: a target behind a hill, or a path the hill closes, is not fired at; the system looks for another.
+                let land = if ready && aligned {
+                    match (sam.terrain_verdict(mt, now), sam.track(mt)) {
+                        (Some(bits), _) => bits,
+                        (None, Some(tr)) => {
+                            let mut bits = terrain::launch_blocks(ground, load.kind, muzzle, sight::antenna(sam), tr.est(now), tr.vel);
+                            if bits == terrain::WAIT {
+                                // The land is being asked for: a moment's wait, not a long one (the game may not answer).
+                                if now.saturating_sub(*sam.waits.entry(mt).or_insert(now)) > terrain::WAIT_TICKS {
+                                    bits = 0;
+                                }
+                            } else {
+                                sam.waits.remove(&mt);
+                                if bits != 0 {
+                                    sam.terrain.insert(mt, (now, bits));
+                                }
+                            }
+                            bits
+                        }
+                        (None, None) => 0,
+                    }
+                } else {
+                    0
+                };
+                if land == terrain::WAIT {
+                    // The land under the shot is not known yet: it waits.
+                } else if land != 0 {
+                    retarget(&mut missile_on, Some(mt), None);
+                    sam.target = None;
+                } else if ready && aligned {
                     launches.push((load.kind, muzzle, dir, mt, sam.id));
                     // Its missile is on it from now, so the systems after this one this tick see
                     // the target taken; this one's next launch looks for another.
@@ -2204,7 +2326,7 @@ impl Sim {
         let now = self.tick;
         let mut done: Vec<(u32, Option<u32>, bool, u32)> = Vec::new(); // (missile, target, kill, sam)
         let (mut missed, mut expired, mut orphaned) = (0u32, 0u32, 0u32);
-        let mut blocked = 0u32;
+        let (mut blocked, mut scrubbed) = (0u32, 0u32);
         let sams_fit: HashMap<u32, f64> = self.sams.iter().map(|s| (s.id, 1.0 - 0.3 * (1.0 - s.health.clamp(0.0, 1.0)))).collect();
         for m in &mut self.missiles {
             m.age += 1;
@@ -2223,7 +2345,14 @@ impl Sim {
                     let los = (t.pos - m.pos).normalize_or_zero();
                     let closing = (speed - t.vel.dot(los)).max(1.0);
                     let tgo = t.pos.distance(m.pos) / closing;
-                    turn(dir, t.pos + t.vel * tgo - m.pos, spec.turn)
+                    // Over the land in the way: lofted as far as the missile can, else it blows up before the ridge.
+                    let (want, fail) = terrain::steer(ground, m.kind, m.pos, speed, t.pos + t.vel * tgo);
+                    if fail {
+                        scrubbed += 1;
+                        done.push((m.id, Some(t.id), false, m.sam));
+                        continue;
+                    }
+                    turn(dir, want, spec.turn)
                 }
                 // After a cold launch it tips over towards the target while the motor burns.
                 Some(t) if lit && spec.cold > 0 => turn(dir, t.pos - m.pos, spec.turn * 0.5),
@@ -2303,6 +2432,7 @@ impl Sim {
             t.expired += expired;
             t.orphaned += orphaned;
             t.blocked += blocked;
+            t.scrubbed += scrubbed;
         });
         for (mid, target, kill, sam) in done {
             if let Some(i) = self.missiles.iter().position(|m| m.id == mid) {
diff --git a/airdef-mod/src/sim/raid.rs b/airdef-mod/src/sim/raid.rs
index c729b4f..fc1a90e 100644
--- a/airdef-mod/src/sim/raid.rs
+++ b/airdef-mod/src/sim/raid.rs
@@ -84,6 +84,12 @@ pub(super) struct Plan {
     approach: Approach,
     total: u32,
     centre: DVec3,
+    /// The land under the grid's cells (NaN where the game has none to tell of), the cells still unanswered, and
+    /// the ticks the planner has waited for the answers. A smart raid is routed over the land, not round it.
+    heights: Vec<f32>,
+    unanswered: Vec<u32>,
+    waited: u32,
+    mapped: bool,
 }
 
 /// The raid in progress: the counts at its start, for the report.
@@ -123,6 +129,20 @@ impl Grid {
 
 /// The cheapest way over `grid` from `from` to `to` by its prices (A*): points along it, `to` last.
 pub(super) fn plan_route(grid: &Grid, prices: &[f32], from: DVec3, to: DVec3) -> (Vec<DVec3>, usize) {
+    plan_route_on(grid, prices, None, from, to)
+}
+
+/// The land a route crosses: its height under each cell (NaN unknown), the climb a kind holds for long
+/// (rise a block), and the height above which the land forces a drone up from its low altitude.
+pub(super) struct Relief<'a> {
+    pub heights: &'a [f32],
+    pub slope: f32,
+    pub floor: f32,
+}
+
+/// [`plan_route`] over relief: a climb steeper than the kind holds is dear (a cliff or a ridge it would have to
+/// pull up over), and high land costs more than a valley, where it can fly low and stay under the radars.
+pub(super) fn plan_route_on(grid: &Grid, prices: &[f32], relief: Option<&Relief>, from: DVec3, to: DVec3) -> (Vec<DVec3>, usize) {
     let mut opened = 0;
     let n = grid.size;
     let at = |(i, j): (i32, i32)| (i * n + j) as usize;
@@ -151,7 +171,21 @@ pub(super) fn plan_route(grid: &Grid, prices: &[f32], from: DVec3, to: DVec3) ->
             }
             let len = if di != 0 && dj != 0 { std::f32::consts::SQRT_2 } else { 1.0 };
             // The target's own cell is where it must go, whatever covers it.
-            let price = if nb == goal { len } else { len * prices[at(nb)] };
+            let mut price = if nb == goal { len } else { len * prices[at(nb)] };
+            if let Some(r) = relief
+                && nb != goal
+            {
+                let (h0, h1) = (r.heights[at(c)], r.heights[at(nb)]);
+                if h1.is_finite() {
+                    price += len * ((h1 - r.floor) / 30.0).clamp(0.0, 4.0);
+                    if h0.is_finite() {
+                        let slope = (h1 - h0) / (len * grid.cell as f32);
+                        if slope > r.slope {
+                            price += (slope - r.slope) * 20.0 * len;
+                        }
+                    }
+                }
+            }
             let ng = g + price;
             if ng < best[at(nb)] {
                 best[at(nb)] = ng;
@@ -250,15 +284,53 @@ impl Sim {
             approach: order.approach,
             total,
             centre,
+            heights: Vec::new(),
+            unanswered: Vec::new(),
+            waited: 0,
+            mapped: !smart,
         });
         // A raid without routes is ready at once.
-        self.plan_step(out);
+        self.plan_step(None, out);
         total
     }
 
     /// Works on the raid's plan a while (a tick's share), and launches it when it is ready.
-    pub(super) fn plan_step(&mut self, out: &mut Out) {
+    pub(super) fn plan_step(&mut self, ground: Option<&mut Ground>, out: &mut Out) {
         let Some(mut plan) = self.plan.take() else { return };
+        // A smart raid first learns the land under its grid: asked for in bulk, a thousand columns a tick, for
+        // up to two seconds (what the game has no land for stays unknown and costs nothing).
+        if !plan.mapped {
+            let Some(ground) = ground else {
+                self.plan = Some(plan);
+                return;
+            };
+            let n = plan.grid.size;
+            if plan.heights.is_empty() {
+                plan.heights = vec![f32::NAN; (n * n) as usize];
+                plan.unanswered = (0..(n * n) as u32).collect();
+            }
+            let Plan { grid, heights, unanswered, .. } = &mut plan;
+            unanswered.retain(|&k| {
+                let (i, j) = (k as i32 / n, k as i32 % n);
+                let c = grid.centre((i, j), 0.0);
+                match ground.column(c.x.floor() as i32, c.z.floor() as i32, 1024) {
+                    None => true,
+                    Some(h) => {
+                        if let Some(h) = h {
+                            heights[k as usize] = h as f32;
+                        }
+                        false
+                    }
+                }
+            });
+            plan.waited += 1;
+            if plan.unanswered.is_empty() || plan.waited >= 40 {
+                plan.mapped = true;
+            } else {
+                self.plan = Some(plan);
+                return;
+            }
+        }
         let mut work = 0usize;
         while plan.next < plan.items.len() && work < WORK_PER_TICK {
             let i = plan.next;
@@ -268,17 +340,39 @@ impl Sim {
             };
             let spec = kind.spec();
             let mut d = plan.items[i].d.clone();
+            // It starts over the land, not in it: a hill under the starting point lifts it.
+            let mut from = from;
+            if !plan.heights.is_empty() {
+                let (gi, gj) = plan.grid.index(from);
+                let g = plan.heights[(gi * plan.grid.size + gj) as usize];
+                let floor = f64::from(g) + if spec.ballistic.is_some() { 10.0 } else { spec.clearance + 10.0 };
+                if g.is_finite() && from.y < floor {
+                    from.y = floor;
+                    d.pos.y = floor;
+                    if spec.ballistic.is_some() {
+                        let flat = horizontal(aim - from);
+                        let time = (flat.length() / spec.speed).max(30.0);
+                        d.vel = flat / time + DVec3::Y * ((aim.y - from.y + 0.5 * GRAVITY * time * time) / time);
+                    }
+                }
+            }
             let mut path = from.distance(aim);
             if let Some(key) = key {
                 let route = match plan.routes.get(&key) {
                     Some(r) => r.clone(),
                     None => {
                         if !plan.prices.contains_key(&kind) {
-                            let (p, cost) = self.price_grid(&plan.grid, kind);
+                            let heights = (!plan.heights.is_empty()).then_some(plan.heights.as_slice());
+                            let (p, cost) = self.price_grid_on(&plan.grid, kind, heights);
                             work += cost;
                             plan.prices.insert(kind, p);
                         }
-                        let (r, cost) = plan_route(&plan.grid, &plan.prices[&kind], from, aim);
+                        let relief = (!plan.heights.is_empty()).then(|| Relief {
+                            heights: &plan.heights,
+                            slope: (kind.climb_pitch().tan() * 0.5) as f32,
+                            floor: (aim.y + spec.clearance) as f32,
+                        });
+                        let (r, cost) = plan_route_on(&plan.grid, &plan.prices[&kind], relief.as_ref(), from, aim);
                         work += cost;
                         plan.routes.insert(key, r.clone());
                         r
@@ -357,6 +451,7 @@ impl Sim {
             jammed: false,
             sector: 0,
             smart: false,
+            nav: Nav::default(),
         }
     }
 
@@ -404,6 +499,12 @@ impl Sim {
     /// The price of each cell of `grid` for this kind flying low: 1, and much more where a
     /// system sees it there (its radar's reach for it, the land) and can shoot it.
     pub(super) fn price_grid(&self, grid: &Grid, kind: DroneKind) -> (Vec<f32>, usize) {
+        self.price_grid_on(grid, kind, None)
+    }
+
+    /// The same over known land: a cell's drone flies `height` over the land there, not over the system's feet,
+    /// so what a radar sees and what a hill hides follow the relief.
+    pub(super) fn price_grid_on(&self, grid: &Grid, kind: DroneKind, land: Option<&[f32]>) -> (Vec<f32>, usize) {
         let mut cost = 0;
         let spec = kind.spec();
         let height = spec.clearance.max(6.0);
@@ -446,7 +547,8 @@ impl Sim {
             for i in (ci - r).max(0)..=(ci + r).min(n - 1) {
                 for j in (cj - r).max(0)..=(cj + r).min(n - 1) {
                     cost += 1;
-                    let p = grid.centre((i, j), s.pos.y + height);
+                    let ground = land.map(|l| l[(i * n + j) as usize]).filter(|g| g.is_finite());
+                    let p = grid.centre((i, j), ground.map_or(s.pos.y + height, |g| f64::from(g) + height));
                     let d = horizontal(p - s.pos).length();
                     if d > far {
                         continue;
diff --git a/airdef-mod/src/sim/record.rs b/airdef-mod/src/sim/record.rs
index 666a5f8..10d2f64 100644
--- a/airdef-mod/src/sim/record.rs
+++ b/airdef-mod/src/sim/record.rs
@@ -65,6 +65,8 @@ pub struct Tally {
     pub ammo_waits: u32,
     /// Interceptors lost against the land or a building on their way.
     pub blocked: u32,
+    /// Interceptors that blew up in the air short of land they could not climb over.
+    pub scrubbed: u32,
 }
 
 impl Tally {
@@ -76,6 +78,7 @@ impl Tally {
             tracks_lost: self.tracks_lost.saturating_sub(start.tracks_lost),
             ammo_waits: self.ammo_waits.saturating_sub(start.ammo_waits),
             blocked: self.blocked.saturating_sub(start.blocked),
+            scrubbed: self.scrubbed.saturating_sub(start.scrubbed),
         }
     }
     /// The non-zero counts as a line, or nothing.
@@ -87,6 +90,7 @@ impl Tally {
             (self.tracks_lost, "потерь трека"),
             (self.ammo_waits, "ожиданий БК"),
             (self.blocked, "ракет разбились о препятствие"),
+            (self.scrubbed, "ракет самоуничтожились у рельефа"),
         ]
         .into_iter()
         .filter(|p| p.0 > 0)
diff --git a/airdef-mod/src/sim/regress.rs b/airdef-mod/src/sim/regress.rs
index 9030f9b..113117e 100644
--- a/airdef-mod/src/sim/regress.rs
+++ b/airdef-mod/src/sim/regress.rs
@@ -187,7 +187,8 @@ fn turret_waits_for_its_aim() {
     sim.sams.push(Sam::new(id, SamKind::Radar, DVec3::new(0.0, 70.0, 0.0), 0.0));
     // Straight behind the turret's heading, a slow target well inside the gun's reach.
     sim.add_drone(DroneKind::Shahed, DVec3::new(0.0, 75.0, 60.0), DVec3::ZERO, DVec3::new(0.0, 70.0, 900.0));
-    sim.drones[0].vel = DVec3::ZERO;
+    // (Pointing away from the gun, so that it doesn't start by turning back over it.)
+    sim.drones[0].vel = DVec3::Z * 0.01;
     let (mut ground, mut out) = (Ground::default(), Out::default());
     let mut turned = 0;
     for _ in 0..200 {
@@ -392,7 +393,9 @@ fn drone_flying_into_a_hill_explodes_at_its_face() {
         let mut sim = Sim::new(3);
         sim.damage = false;
         let mut ground = Ground::default();
-        sim.add_drone(kind, DVec3::new(0.0, 80.0, 0.0), DVec3::X, DVec3::new(600.0, 80.0, 0.0));
+        // The aim is on the far side of the face, close enough that the dive is not called off for the hill (it is
+        // below, at the end of the dive, where flight planning leaves it alone).
+        sim.add_drone(kind, DVec3::new(0.0, 80.0, 0.0), DVec3::X, DVec3::new(80.0, 80.0, 0.0));
         sim.drones[0].flight = Flight::Dive;
         for _ in 0..300 {
             if sim.drones.is_empty() {
@@ -547,3 +550,251 @@ fn fires_start_merge_and_are_limited() {
     assert!(fl > 0.0 && sm > 0.0);
     assert_eq!(fires::level(3000.0, 3000.0).0, 0.0);
 }
+
+// ---- flight over the land: strike drones follow it, launchers keep their missiles for shots the land allows,
+// interceptors keep clear of it. A synthetic land (a height function) stands in for the game.
+
+/// Land from a height function: blocks below it are solid, and the game's height map says the same.
+struct Land<F: Fn(i32, i32) -> i32>(F);
+impl<F: Fn(i32, i32) -> i32> world::WorldSource for Land<F> {
+    fn solid(&self, x: i32, y: i32, z: i32) -> Option<bool> {
+        Some(y < (self.0)(x, z))
+    }
+}
+
+/// What the game answers a tick after the sim asked: land heights, and the sections it needs.
+fn answer_land<F: Fn(i32, i32) -> i32>(ground: &mut Ground, land: &Land<F>, now: u64) {
+    let columns = ground.take_wanted().into_iter().map(|(x, z)| (x, z, (land.0)(x, z))).collect();
+    ground.answer(columns, now);
+    let sections = ground.world.take_wanted(now);
+    ground.world.serve(land, sections, now);
+}
+
+/// A ridge across the way, `rise` blocks high over a flat at 64, `half` blocks of slope to each side, crest at x=300.
+fn ridge(rise: i32, half: i32) -> Land<impl Fn(i32, i32) -> i32> {
+    ridge_at(300, rise, half)
+}
+
+fn ridge_at(crest: i32, rise: i32, half: i32) -> Land<impl Fn(i32, i32) -> i32> {
+    Land(move |x, _| 64 + (rise - (x - crest).abs() * rise / half).max(0))
+}
+
+/// Flies one drone of `kind` along +x over `land` from x=0 to its aim at x=750, to the end. Returns the sim.
+fn fly_over<F: Fn(i32, i32) -> i32>(kind: DroneKind, land: &Land<F>, low: bool) -> Sim {
+    let mut sim = Sim::new(5);
+    sim.damage = false;
+    let mut ground = Ground::default();
+    let spec = kind.spec();
+    let height = if spec.cruise > 0.0 { spec.cruise } else { 25.0 };
+    sim.add_drone(kind, DVec3::new(0.0, 64.0 + height, 0.0), DVec3::X, DVec3::new(750.0, 64.0, 0.0));
+    sim.drones[0].low = low;
+    for _ in 0..4 {
+        sim.tick += 1;
+        answer_land(&mut ground, land, sim.tick);
+    }
+    let mut out = Out::default();
+    for _ in 0..4000 {
+        if sim.drones.is_empty() {
+            break;
+        }
+        sim.tick += 1;
+        sim.step_drones(&mut ground, None, &mut out);
+        answer_land(&mut ground, land, sim.tick);
+    }
+    sim
+}
+
+// Strike drones climb over a hill they could not have seen 20 blocks ahead.
+#[test]
+fn a_raid_crossing_a_hill_flies_over_it() {
+    for (rise, half) in [(60, 100), (60, 60), (90, 120)] {
+        let land = ridge(rise, half);
+        for kind in [DroneKind::Shahed, DroneKind::Geran3, DroneKind::Lancet, DroneKind::Gerbera, DroneKind::Kh101, DroneKind::Kalibr, DroneKind::Kh22, DroneKind::Zircon] {
+            for low in [false, true] {
+                let sim = fly_over(kind, &land, low);
+                assert!(sim.drones.is_empty(), "{kind:?}: still flying");
+                // It bursts at its aim, not on the hill 450 blocks short of it (where a crash or a decoy's end shows too).
+                let at = sim.blasts.first().expect("no blast").at;
+                assert!(at.x > 700.0, "{kind:?} low={low} burst at x={:.0} over a {rise}-block hill ({half} to the crest)", at.x);
+            }
+        }
+    }
+}
+
+// A low drone hugs the land: it does not fly at cruise height over the flat behind the ridge.
+#[test]
+fn a_low_drone_hugs_the_land_after_the_ridge() {
+    let land = ridge(60, 100);
+    let mut sim = Sim::new(5);
+    sim.damage = false;
+    let mut ground = Ground::default();
+    sim.add_drone(DroneKind::Shahed, DVec3::new(0.0, 75.0, 0.0), DVec3::X, DVec3::new(900.0, 64.0, 0.0));
+    sim.drones[0].low = true;
+    let mut out = Out::default();
+    let mut highest_after = 0.0f64;
+    for _ in 0..4000 {
+        if sim.drones.is_empty() {
+            break;
+        }
+        sim.tick += 1;
+        sim.step_drones(&mut ground, None, &mut out);
+        answer_land(&mut ground, &land, sim.tick);
+        if let Some(d) = sim.drones.first()
+            && d.pos.x > 560.0
+            && d.pos.x < 800.0
+        {
+            highest_after = highest_after.max(d.pos.y);
+        }
+    }
+    assert_eq!(sim.crashes, 0);
+    assert!(highest_after < 64.0 + 40.0, "still {highest_after:.0} high far behind the ridge");
+}
+
+/// A target flying slowly along the ridge's far side at `x`, with a radar on the crest to see it.
+fn behind_ridge(land: &Land<impl Fn(i32, i32) -> i32>, crest: i32, kind: SamKind, x: f64, ticks: u32) -> Sim {
+    let mut sim = Sim::new(9);
+    sim.damage = false;
+    let ground_y = (land.0)(0, 0) as f64;
+    let id = sim.id();
+    sim.sams.push(Sam::new(id, kind, DVec3::new(0.0, ground_y, 0.0), 0.0));
+    let id = sim.id();
+    sim.sams.push(Sam::new(id, SamKind::Radar, DVec3::new(f64::from(crest), (land.0)(crest, 0) as f64, -60.0), 0.0));
+    let mut ground = Ground::default();
+    let mut out = Out::default();
+    for _ in 0..40 {
+        sim.tick += 1;
+        answer_land(&mut ground, land, sim.tick);
+    }
+    // It crawls along the far side of the ridge, 20 blocks over the land.
+    let there = (land.0)(x as i32, 0) as f64;
+    sim.add_drone(DroneKind::Gerbera, DVec3::new(x, there + 20.0, -100.0), DVec3::Z, DVec3::new(x, there, 3000.0));
+    for _ in 0..ticks {
+        sim.step(&mut ground, None, &mut out);
+        answer_land(&mut ground, land, sim.tick);
+    }
+    sim
+}
+
+// A short-range system behind a hill does not fire at a target the hill masks from it, whatever the network says.
+#[test]
+fn a_system_does_not_fire_at_a_target_masked_by_a_hill() {
+    // A short-range system 250 blocks short of the crest, the target 80 blocks beyond it.
+    type Boxed = Land<Box<dyn Fn(i32, i32) -> i32>>;
+    let hill: Boxed = Land(Box::new(|x, _| 64 + (60 - (x - 150).abs()).max(0)));
+    let flat: Boxed = Land(Box::new(|_, _| 64));
+    let shot = |land: &Boxed| {
+        let mut sim = Sim::new(9);
+        sim.damage = false;
+        let id = sim.id();
+        sim.sams.push(Sam::new(id, SamKind::Tor, DVec3::new(100.0, 64.0, 0.0), 0.0));
+        let id = sim.id();
+        sim.sams.push(Sam::new(id, SamKind::Radar, DVec3::new(150.0, (land.0)(150, 0) as f64, -60.0), 0.0));
+        let mut ground = Ground::default();
+        let mut out = Out::default();
+        for _ in 0..40 {
+            sim.tick += 1;
+            answer_land(&mut ground, land, sim.tick);
+        }
+        sim.add_drone(DroneKind::Gerbera, DVec3::new(200.0, 84.0, -60.0), DVec3::Z, DVec3::new(200.0, 64.0, 3000.0));
+        let mut masked = 0u32;
+        let mut seen = false;
+        let mut told = false;
+        for _ in 0..300 {
+            sim.step(&mut ground, None, &mut out);
+            answer_land(&mut ground, land, sim.tick);
+            seen |= sim.sams[0].seen.len() == 1;
+            masked += sim.sams[0].terrain.values().filter(|(_, b)| *b == terrain::MASKED).count() as u32;
+            // `why` names the reason while the verdict stands.
+            told |= sim.why(0).iter().any(|c| !c.ok && c.text.contains("за рельефом"));
+        }
+        (sim, seen, masked, told)
+    };
+    let (open, seen, _, _) = shot(&flat);
+    assert!(seen && open.sams[0].fired > 0, "control: with a clear line the Tor must fire (seen {seen}, fired {})", open.sams[0].fired);
+    let (shut, seen, masked, told) = shot(&hill);
+    assert!(seen, "the network must have shown the target to the Tor");
+    assert_eq!(shut.sams[0].fired, 0, "the Tor fired at a target behind the hill");
+    assert!(masked > 0, "no launch was judged and refused for the land");
+    assert_eq!(shut.tally.blocked + shut.tally.scrubbed, 0);
+    assert!(told, "`why` never named the land as the reason");
+}
+
+// A long-range system lofts over a low ridge (its interceptor does not hit it) but not over a mountain.
+#[test]
+fn a_long_range_system_lofts_over_a_ridge_or_waits() {
+    let low = ridge_at(150, 25, 60);
+    let sim = behind_ridge(&low, 150, SamKind::IrisT, 230.0, 300);
+    assert!(sim.sams[0].fired > 0, "an IRIS-T SLM must loft over a 25-block ridge");
+    assert_eq!(sim.tally.blocked + sim.tally.scrubbed, 0, "its interceptors hit the ridge");
+    let tall = ridge_at(150, 400, 100);
+    let sim = behind_ridge(&tall, 150, SamKind::IrisT, 230.0, 300);
+    assert_eq!(sim.sams[0].fired, 0, "no missile can climb a 400-block mountain at this range");
+    assert_eq!(sim.tally.blocked + sim.tally.scrubbed, 0);
+    assert!(sim.why(0).iter().any(|c| !c.ok && c.text.contains("рельеф")), "{:?}", sim.why(0).iter().map(|c| &c.text).collect::<Vec<_>>());
+}
+
+// Interceptors fly over rolling land at a target low over it, and none ends in the ground.
+#[test]
+fn an_interceptor_over_rolling_land_does_not_hit_the_ground() {
+    let rolling = Land(|x: i32, z: i32| 70 + (28.0 * ((f64::from(x) / 21.0).sin() + (f64::from(z) / 33.0).cos()) / 2.0).round() as i32);
+    for kind in [MissileKind::Pac3, MissileKind::M48n6, MissileKind::IrisT, MissileKind::M57e6, MissileKind::M9m338, MissileKind::P1sun] {
+        for dx in [160.0, 260.0, 380.0] {
+            let mut sim = Sim::new(4);
+            sim.damage = false;
+            let mut ground = Ground::default();
+            let mut out = Out::default();
+            for _ in 0..4 {
+                sim.tick += 1;
+                answer_land(&mut ground, &rolling, sim.tick);
+            }
+            // A Gerbera 20 blocks over the land at the far end, flying away from the launcher.
+            let at = DVec3::new(dx, (rolling.0)(dx as i32, 0) as f64 + 20.0, 0.0);
+            sim.add_drone(DroneKind::Gerbera, at, DVec3::X, DVec3::new(5000.0, 64.0, 0.0));
+            let (target, id) = (sim.drones[0].id, sim.id());
+            let from = DVec3::new(0.0, (rolling.0)(0, 0) as f64 + 3.0, 0.0);
+            sim.drones[0].engaged = 1;
+            sim.missiles.push(Missile { id, kind, pos: from, vel: DVec3::new(0.5, 0.8, 0.0).normalize() * 0.8, target, sam: 0, age: 0 });
+            for _ in 0..500 {
+                if sim.missiles.is_empty() {
+                    break;
+                }
+                sim.tick += 1;
+                sim.step_missiles(&mut ground, &mut out);
+                answer_land(&mut ground, &rolling, sim.tick);
+            }
+            assert!(sim.missiles.is_empty(), "{kind:?} at {dx}: still flying");
+            assert_eq!(sim.tally.blocked, 0, "{kind:?} at {dx}: the interceptor hit the ground");
+        }
+    }
+}
+
+// An interceptor with no way over the land blows up in the air, and that is counted.
+#[test]
+fn an_interceptor_without_a_way_over_blows_up_high() {
+    let wall = ridge(300, 40);
+    let mut sim = Sim::new(4);
+    sim.damage = false;
+    let mut ground = Ground::default();
+    let mut out = Out::default();
+    for _ in 0..4 {
+        sim.tick += 1;
+        answer_land(&mut ground, &wall, sim.tick);
+    }
+    sim.add_drone(DroneKind::Gerbera, DVec3::new(420.0, 90.0, 0.0), DVec3::X, DVec3::new(5000.0, 64.0, 0.0));
+    let (target, id) = (sim.drones[0].id, sim.id());
+    sim.drones[0].engaged = 1;
+    sim.missiles.push(Missile { id, kind: MissileKind::M57e6, pos: DVec3::new(230.0, 70.0, 0.0), vel: DVec3::X * 3.0, target, sam: 0, age: 20 });
+    for _ in 0..200 {
+        if sim.missiles.is_empty() {
+            break;
+        }
+        sim.tick += 1;
+        sim.step_missiles(&mut ground, &mut out);
+        answer_land(&mut ground, &wall, sim.tick);
+    }
+    assert!(sim.missiles.is_empty());
+    assert_eq!((sim.tally.scrubbed, sim.tally.blocked), (1, 0), "{:?}", sim.tally);
+    assert_eq!(sim.drones[0].engaged, 0);
+    let at = sim.blasts.first().expect("no blast").at;
+    assert!(at.y > (wall.0)(at.x as i32, 0) as f64 + 3.0, "it burst in the ground at {at:?}");
+}
diff --git a/airdef-mod/src/sim/terrain.rs b/airdef-mod/src/sim/terrain.rs
new file mode 100644
index 0000000..1827e1e
--- /dev/null
+++ b/airdef-mod/src/sim/terrain.rs
@@ -0,0 +1,344 @@
+//! Flights and the land. Strike drones follow the terrain with a look-ahead worth several seconds of flight
+//! (what they can still climb is a question of their speed and turn rate), dive only down a clear line, and
+//! interceptors keep a safety height over the land ahead, loft over a ridge when the line is blocked, and
+//! blow up high when there is no way over. The launch predicates (`why`) ask the same questions of a
+//! shot before it is fired, so a system doesn't spend missiles on targets behind a hill.
+//!
+//! The land comes from `Ground::land`: heights sampled on a coarse lattice, so many flights share columns and
+//! the questions to the game stay few; what the heights miss (trees, buildings, overhangs) is caught by a
+//! probe through the block cache.
+use super::*;
+
+/// Land heights are sampled at the centres of cells this wide.
+const LATTICE: i32 = 8;
+/// Land questions waiting at once: flights ask for more than a tick can send, and wait.
+const ASK_MAX: usize = 192;
+
+/// What the game has said of the land at a place.
+#[derive(Clone, Copy, PartialEq, Debug)]
+pub(super) enum Rise {
+    /// Not yet: asked.
+    Pending,
+    /// There is no land to tell of (no chunk).
+    Void,
+    /// One above the highest solid block.
+    At(f64),
+}
+
+impl Ground {
+    /// One above the highest solid block at the lattice cell holding `p`, if known; asked for when it isn't.
+    /// Unlike `at` it never asks again for a column it has, and it leaves room for the questions that matter more.
+    pub fn land(&mut self, p: DVec3) -> Option<f64> {
+        match self.rise(p) {
+            Rise::At(g) => Some(g),
+            _ => None,
+        }
+    }
+
+    /// The same, saying whether the game has not answered yet or has no land there to tell of.
+    pub(super) fn rise(&mut self, p: DVec3) -> Rise {
+        let key = (
+            (p.x.floor() as i32).div_euclid(LATTICE) * LATTICE + LATTICE / 2,
+            (p.z.floor() as i32).div_euclid(LATTICE) * LATTICE + LATTICE / 2,
+        );
+        match self.known.get(&key) {
+            Some(&(y, _)) if y > -64 => Rise::At(f64::from(y)),
+            Some(_) => Rise::Void,
+            None => {
+                if self.wanted.len() < ASK_MAX && self.asked.insert(key) {
+                    self.wanted.push(key);
+                }
+                Rise::Pending
+            }
+        }
+    }
+
+    /// The land's height at a column for the raid planner: `None` while the game hasn't answered, `Some(None)`
+    /// where it has no land to tell of. Asks, up to `cap` questions waiting.
+    pub(super) fn column(&mut self, x: i32, z: i32, cap: usize) -> Option<Option<f64>> {
+        match self.known.get(&(x, z)) {
+            Some(&(y, _)) => Some((y > -64).then_some(f64::from(y))),
+            None => {
+                if self.wanted.len() < cap && self.asked.insert((x, z)) {
+                    self.wanted.push((x, z));
+                }
+                None
+            }
+        }
+    }
+}
+
+/// What a flight can do about a rise ahead.
+#[derive(Clone, Copy, Debug)]
+pub(super) struct Climb {
+    /// Radius of its tightest pull-up (blocks).
+    pub radius: f64,
+    /// The steepest climb it holds (radians).
+    pub pitch: f64,
+}
+
+impl Climb {
+    /// How much height it can have gained by the time it has gone `s` blocks on, starting level.
+    pub fn gain(&self, s: f64) -> f64 {
+        let arc = self.radius * self.pitch.sin();
+        if s <= arc {
+            self.radius - (self.radius * self.radius - s * s).max(0.0).sqrt()
+        } else {
+            self.radius * (1.0 - self.pitch.cos()) + (s - arc) * self.pitch.tan()
+        }
+    }
+}
+
+impl DroneKind {
+    /// The steepest climb it holds in cruise (radians): cruise missiles are the shallowest.
+    pub(super) fn climb_pitch(self) -> f64 {
+        match self {
+            DroneKind::Kh101 | DroneKind::Kalibr => 0.45,
+            DroneKind::Lancet => 0.7,
+            DroneKind::Geran3 | DroneKind::Kh22 => 0.6,
+            _ => 0.5,
+        }
+    }
+    pub(super) fn climb(self) -> Climb {
+        let s = self.spec();
+        Climb { radius: (s.speed / s.turn.max(0.01) * 1.15).max(12.0), pitch: self.climb_pitch() }
+    }
+    /// Blocks it looks ahead: eight seconds of flight, at least a pull-up and a climb over a hill.
+    pub(super) fn look_len(self) -> f64 {
+        let s = self.spec();
+        (s.speed * 160.0).clamp(160.0, 900.0)
+    }
+}
+
+/// A flight's new heading: it turns in yaw towards `heading` and in pitch towards a climb of `slope`, together
+/// at most `rate` radians a tick, so a turn on to a new course doesn't dip or climb by itself (a great-circle
+/// turn between nearly opposite headings can go either way). With `climb` set the pitch comes first and the
+/// yaw gets what is left of the rate.
+pub(super) fn fly_towards(old: DVec3, heading: DVec3, slope: f64, rate: f64, climb: bool) -> DVec3 {
+    let (old_yaw, old_pitch) = (old.x.atan2(old.z), old.y.clamp(-1.0, 1.0).asin());
+    let want_yaw = heading.x.atan2(heading.z);
+    let mut yaw = angle_diff(old_yaw, want_yaw);
+    let mut pitch = slope.atan() - old_pitch;
+    if climb {
+        pitch = pitch.clamp(-rate, rate);
+        yaw = yaw.clamp(-(rate * rate - pitch * pitch).max(0.0).sqrt(), (rate * rate - pitch * pitch).max(0.0).sqrt());
+    } else {
+        let total = yaw.hypot(pitch);
+        if total > rate {
+            yaw *= rate / total;
+            pitch *= rate / total;
+        }
+    }
+    let (yaw, pitch) = (old_yaw + yaw, old_pitch + pitch);
+    DVec3::new(yaw.sin() * pitch.cos(), pitch.sin(), yaw.cos() * pitch.cos())
+}
+
+/// How far over the land a dive's line passes.
+pub(super) const DIVE_MARGIN: f64 = 8.0;
+
+/// `v` with its pitch held between `lo` and `hi` (radians); `level` is the way it faces if it points straight up or down.
+pub(super) fn clamp_pitch(v: DVec3, lo: f64, hi: f64, level: DVec3) -> DVec3 {
+    let pitch = v.y.clamp(-1.0, 1.0).asin();
+    if (lo..=hi).contains(&pitch) {
+        return v;
+    }
+    let pitch = pitch.clamp(lo, hi);
+    horizontal(v).normalize_or(level) * pitch.cos() + DVec3::Y * pitch.sin()
+}
+
+/// Distances ahead where the land is sampled.
+const REACH: [f64; 21] = [
+    0.0, 8.0, 16.0, 24.0, 32.0, 44.0, 56.0, 72.0, 90.0, 112.0, 136.0, 164.0, 196.0, 232.0, 272.0, 316.0, 366.0, 424.0, 500.0, 600.0,
+    720.0,
+];
+
+/// The height a flight must be at *now* to clear the land along each of `lines` (a unit horizontal direction and
+/// how far out to look) by `clear`, given what it can climb: the greatest over the samples of the land's height plus clearance
+/// less the height it can gain on the way. `None` when nothing is known.
+pub(super) fn required_height(ground: &mut Ground, pos: DVec3, lines: &[(DVec3, f64)], clear: f64, climb: &Climb) -> Option<f64> {
+    let mut need: Option<f64> = None;
+    for &(dir, len) in lines {
+        for &s in REACH.iter().chain(&[900.0]) {
+            if s > len {
+                break;
+            }
+            if let Some(g) = ground.land(pos + dir * s) {
+                let h = g + clear - climb.gain(s);
+                need = Some(need.map_or(h, |n: f64| n.max(h)));
+            }
+        }
+    }
+    need
+}
+
+/// The least height to start from, over here, so that the straight line down to `target` stays `margin` over the
+/// land (the last stretch before the aim is the target's own business). `None` when the land isn't known.
+pub(super) fn dive_height(ground: &mut Ground, pos: DVec3, target: DVec3, margin: f64) -> Option<f64> {
+    let flat = horizontal(target - pos);
+    let total = flat.length();
+    if total < 20.0 {
+        return None;
+    }
+    let dir = flat / total;
+    let mut need: Option<f64> = None;
+    let n = ((total - 14.0) / 12.0).clamp(1.0, 40.0) as i32;
+    for k in 0..=n {
+        let s = (total - 14.0) * f64::from(k) / f64::from(n);
+        if let Some(g) = ground.land(pos + dir * s) {
+            let f = s / total;
+            let y = (g + margin - target.y * f) / (1.0 - f);
+            need = Some(need.map_or(y, |m: f64| m.max(y)));
+        }
+    }
+    need
+}
+
+/// The slope (rise a block) a flight at `from` must hold to clear the land by `margin` on its way towards
+/// `to`, with a pull-up of `radius` for the climb to begin early, ignoring the last `skip` blocks before `to`.
+/// Returns the slope and how far away the land that asks for it is; `None` when nothing is in the way or known.
+pub(super) fn rope(ground: &mut Ground, from: DVec3, to: DVec3, margin: f64, radius: f64, (near, reach, skip): (f64, f64, f64), pending: &mut bool) -> Option<(f64, f64)> {
+    let flat = horizontal(to - from);
+    let total = flat.length();
+    if total < 1.0 {
+        return None;
+    }
+    let dir = flat / total;
+    let end = (total - skip).min(reach);
+    let mut best: Option<(f64, f64)> = None;
+    let mut s = near;
+    while s <= end {
+        match ground.rise(from + dir * s) {
+            Rise::At(g) => {
+                let slope = (g + margin - from.y) / (s - radius * 0.6).max(6.0);
+                if best.is_none_or(|b| slope > b.0) {
+                    best = Some((slope, s));
+                }
+            }
+            Rise::Pending => *pending = true,
+            Rise::Void => {}
+        }
+        s += if s < 64.0 { 8.0 } else { 16.0 };
+    }
+    best
+}
+
+// ---------------------------------------------------------------- interceptors
+
+impl MissileKind {
+    /// The steepest climb it flies to get over land (radians): long-range missiles loft, short-range ones don't.
+    pub(super) fn loft(self) -> f64 {
+        match self {
+            MissileKind::M77n6 => 1.25,
+            MissileKind::M48n6 => 1.1,
+            MissileKind::Pac3 | MissileKind::IrisT | MissileKind::Amraam => 0.9,
+            MissileKind::M9m317 => 0.8,
+            MissileKind::P1sun => 0.5,
+            MissileKind::M57e6 | MissileKind::M9m338 => 0.3,
+        }
+    }
+    /// Whether it lofts over a ridge to a target behind it.
+    pub(super) fn lofts(self) -> bool {
+        self.loft() >= 0.5
+    }
+}
+
+/// How high above the land an interceptor keeps.
+pub(super) const MISSILE_MARGIN: f64 = 8.0;
+
+/// What keeps an interceptor from being launched at a target for the land in the way.
+pub(super) const MASKED: u8 = 1;
+pub(super) const PATH_BLOCKED: u8 = 2;
+/// The land under the line of fire has been asked for and not answered: the shot waits a tick or two.
+pub(super) const WAIT: u8 = 4;
+/// Ticks a shot waits for the land to be answered before it is judged on what is known.
+pub(super) const WAIT_TICKS: u64 = 30;
+
+/// Whether a shot from `muzzle` (launcher at `antenna`) at a target forecast at `est` moving at `vel` may be
+/// fired for the land: the intercept point must not be behind a hill from the launcher, unless the missile
+/// lofts, and the path the missile would fly must be clear.
+pub(super) fn launch_blocks(ground: &mut Ground, kind: MissileKind, muzzle: DVec3, antenna: DVec3, est: DVec3, vel: DVec3) -> u8 {
+    let spec = kind.spec();
+    // Where it meets the target: the forecast carried on for the flight time.
+    let mut at = est;
+    for _ in 0..2 {
+        let tgo = muzzle.distance(at) / (spec.speed * 0.8);
+        at = est + vel * tgo;
+    }
+    let flat = horizontal(at - antenna);
+    let total = flat.length();
+    if total < 40.0 {
+        return 0;
+    }
+    let dir = flat / total;
+    // The line of sight from the launcher: any rise of the land over the line to the intercept point masks it.
+    let mut masked = false;
+    let mut waiting = false;
+    let mut s = 12.0;
+    while s < total - 12.0 {
+        match ground.rise(antenna + dir * s) {
+            Rise::At(g) if g + 1.0 > antenna.y + (at.y - antenna.y) * s / total => {
+                masked = true;
+                break;
+            }
+            Rise::Pending => waiting = true,
+            _ => {}
+        }
+        s += 16.0;
+    }
+    if !masked && waiting {
+        return WAIT;
+    }
+    if !masked {
+        return 0;
+    }
+    if !kind.lofts() {
+        return MASKED;
+    }
+    // A lofted path: climbs at the slope the highest land in the way asks for, and comes down on the target.
+    let radius = spec.speed / spec.turn.max(0.05);
+    let mut pending = false;
+    let path = rope(ground, muzzle, at, MISSILE_MARGIN, radius, (32.0, total, 24.0), &mut pending);
+    match path {
+        Some((slope, _)) if slope > kind.loft().tan() => PATH_BLOCKED,
+        _ if pending => WAIT,
+        _ => 0,
+    }
+}
+
+impl Sam {
+    /// What the land said of a shot at `target` when it was last judged, if lately.
+    pub(super) fn terrain_verdict(&self, target: u32, now: u64) -> Option<u8> {
+        self.terrain.get(&target).filter(|(when, _)| now.saturating_sub(*when) <= VERDICT_AGE).map(|(_, bits)| *bits)
+    }
+}
+
+/// Ticks a launch verdict (the land in the way) is kept before the shot is judged again.
+pub(super) const VERDICT_AGE: u64 = 20;
+
+/// Which way an interceptor steers to keep clear of the land: `aim` is where it would go; the result is a direction
+/// (unit) raised as far as its loft allows, and whether the land is in the way beyond that.
+pub(super) fn steer(ground: &mut Ground, kind: MissileKind, pos: DVec3, speed: f64, aim: DVec3) -> (DVec3, bool) {
+    let spec = kind.spec();
+    let want = (aim - pos).normalize_or(DVec3::Y);
+    let flat = horizontal(want);
+    let flat_len = flat.length();
+    let reach = (speed * 18.0).clamp(60.0, 320.0);
+    let radius = speed / spec.turn.max(0.05);
+    let Some((slope, at)) = rope(ground, pos, aim, MISSILE_MARGIN, radius, (8.0, reach, 20.0), &mut false) else { return (want, false) };
+    let wanted = if flat_len > 1e-6 { want.y / flat_len } else { f64::INFINITY };
+    if slope <= wanted {
+        return (want, false);
+    }
+    let cap = kind.loft().tan();
+    let dir = flat.normalize_or(DVec3::X);
+    let raised = (dir + DVec3::Y * slope.min(cap)).normalize();
+    // No way over, and the land close enough ahead that the next ticks will end in it: blow up before.
+    let mut fail = false;
+    if slope > cap + 0.02 && at < (speed * 6.0).max(40.0) {
+        fail = (1..=4).any(|k| {
+            let p = pos + raised * speed * f64::from(k);
+            ground.land(p).is_some_and(|g| g + 2.0 > p.y)
+        });
+    }
+    (raised, fail)
+}
diff --git a/airdef-mod/src/sim/why.rs b/airdef-mod/src/sim/why.rs
index 6f44a2b..1cf1987 100644
--- a/airdef-mod/src/sim/why.rs
+++ b/airdef-mod/src/sim/why.rs
@@ -308,7 +308,19 @@ impl Sim {
             let aligned = missile_aligned(spec.family, sam.yaw, mount, Some(est), t.id, t.id, err);
             let turn = if vertical { "вертикальный старт" } else { "доворот" };
             v.push(check(aligned, format!("{turn}: ошибка наведения {:.0}°{}", err.to_degrees(), if aligned { "" } else { " — ещё доворачивается" })));
-            fires |= reach == 0 && free < need && mb == 0 && aligned && blocks == 0;
+            // The land: the verdict the launch decision gave this target (`terrain::launch_blocks`) a moment ago.
+            let land = sam.terrain_verdict(t.id, now).unwrap_or(0);
+            if land != 0 {
+                v.push(check(
+                    false,
+                    if land & terrain::MASKED != 0 {
+                        "рельеф: цель за рельефом — ракета не стартует, ждём, пока цель выйдет из-за него"
+                    } else {
+                        "рельеф: траектория перекрыта рельефом — подняться над ним ракета не может"
+                    },
+                ));
+            }
+            fires |= reach == 0 && free < need && mb == 0 && aligned && blocks == 0 && land == 0;
         }
         if let Some(gun) = &spec.gun {
             let on_it = guns_on.get(&t.id).copied().unwrap_or(0) - u32::from(sam.gun_target == Some(t.id));
diff --git a/airdef-mod/src/sim/world.rs b/airdef-mod/src/sim/world.rs
index ec4c5d9..2f69728 100644
--- a/airdef-mod/src/sim/world.rs
+++ b/airdef-mod/src/sim/world.rs
@@ -94,6 +94,8 @@ pub struct WorldCache {
     /// Sections asked, and when.
     asked: HashMap<Sec, u64>,
     epoch: u32,
+    /// Sweeps made as a look ahead (flight planning) ask for sections after the urgent ones.
+    quiet: bool,
     pub stats: WorldStats,
 }
 
@@ -277,7 +279,7 @@ impl WorldCache {
         let s = sec_of(x, y, z);
         if *last != Some(s) {
             *last = Some(s);
-            self.touch(s, true, now);
+            self.touch(s, !self.quiet, now);
         }
         match &self.secs.get(&s)?.fill {
             Fill::Unknown => None,
@@ -301,6 +303,15 @@ impl WorldCache {
         self.solid(&mut None, x, y, z, now) == Some(true)
     }
 
+    /// A sweep made to plan a flight, not to move one: the sections it needs are asked after the urgent ones,
+    /// and a start inside a block is not a hit.
+    pub fn probe(&mut self, a: DVec3, b: DVec3, now: u64) -> Sweep {
+        self.quiet = true;
+        let r = self.sweep(a, b, true, now);
+        self.quiet = false;
+        r
+    }
+
     /// The first solid block along `a` to `b`, by walking the blocks it
     /// crosses; `skip_start` ignores the block it starts in (a launch from a
     /// pad that is part of the land).