The problem: the ballistic equation

A round from a tank gun does not fly straight — it draws a parabola. Variables that shape it:

  • Range — the further, the more drop.
  • Round type — APFSDS is flat-flying (1,700 m/s), HEAT is slow (1,000 m/s), HE in between.
  • Temperature — cold propellant = less thrust, hot = more.
  • Propellant age — storage time changes energy.
  • Air pressure and wind — especially at long range.
  • Own motion — horizontal and vertical velocity components.
  • Target motion — where will the target be by the time the round arrives?
  • Coriolis and tilt — relevant beyond 3 km.
  • Barrel droop — a hot barrel sags in the sun, straightens as it cools.

You have to solve nine variables in 2-3 seconds. No mathematicians on the crew. The solution: FCS — the fire control computer does it for you.

FCS — laser + ballistic computer + stabilizer
  1. 1Gunner's primary sight (GPS)
  2. 2Laser rangefinder (LRF)
  3. 3Ballistic computer
  4. 4Stabilized main gun
  5. 5Crosswind / air sensor
  6. 6Commander's independent sight

The four components of an FCS

1. Laser rangefinder (LRF)

Modern tanks have used Nd:YAG or CO₂ laser rangefinders since the 1970s. A laser pulse goes out, the return travel time is measured. Accuracy: ±5 m, up to 10 km. The M1A2's "eye-safe" laser at 1550 nm cannot be detected by hostile optics and won't damage the crew's eyes.

Thermal sight — 2400 m target acquisition
  1. 1Germanium front objective
  2. 2IR detector array (FPA)
  3. 3Cryocooler dewar
  4. 4Processing electronics
  5. 5Gunner eyepiece
  6. 6IR optical path

2. Thermal imaging (FLIR)

2nd-gen FLIR (Abrams CITV, Leopard 2A6 PERI-R17A2) reads temperature differences.

  • No night — thermals always work.
  • Sees through fog, smoke and dust (unlike visible light).
  • Camouflage usually fails; hot engines and exhausts always glow.
  • Effective detection range: 1.5 km on a person, 4-6 km on a tank.

3. Ballistic computer

The heart of the FCS. Inputs:

  • Range from the LRF.
  • Selected round type.
  • Temperature + pressure sensors.
  • Anemometer (on the turret, real-time wind).
  • Tank gyros for own motion vector.
  • Tracking system for target motion vector.
  • Barrel droop sensor.

Output: how far to elevate and traverse the gun. That value goes straight to the stabilizer that drives the gun.

4. Two-axis stabilizer

Even at 40 km/h over rough ground, the barrel stays locked on target. Hydraulic or electric servos, gyroscopic reference, continuous correction. "Hunting" — the small horizontal-vertical oscillation — is kept under 0.25 mil (0.014°).

Hunter-killer doctrine

The real advantage of modern MBTs: commander and gunner work in parallel.

  • Commander: finds a target through an independent 360° panoramic sight (Abrams CITV, Leo 2 PERI), lases it.
  • Presses a button — the turret slews to that target automatically.
  • Gunner: target is already centered, completes the shot.
  • Commander is already searching for the next target.

This "hunt + kill" cycle produced kill ratios above 10:1 against Iraqi T-72 crews in Desert Storm.

Generations compared

Gen 2 FCS (1980s)

  • Passive night vision (image intensifier).
  • Analog ballistic computer.
  • Single-axis stabilizer.
  • On-the-move hit rate: ~50%.

Gen 3 FCS (1990-2010)

  • Thermal imaging.
  • Digital ballistic computer.
  • Two-axis stabilizer.
  • On-the-move hit rate: ~85%+.

Gen 4 FCS (2015+)

  • AI-assisted target recognition (auto target classification).
  • Sensor fusion: thermal + visible + radar into one HUD.
  • Shared targeting from drones, helicopters and other units.
  • Hunter-killer-killer: commander + gunner + AI as three parallel processes.
  • On-the-move hit rate: 95%+ with fire-and-forget guided rounds (Israel's LAHAT, Russia's 9M119 Refleks).

The numbers — 1980 to today

  • Time to first hit: 12 s → 3 s
  • Detection range: 1 km → 6+ km
  • On-the-move hit rate: 50% → 95%
  • Targets tracked simultaneously: 1 → 16+

The FCS is the real weapon

A 125 mm gun is just a mechanism that pulls a trigger. The real weapon is the system that decides to pull it: optics + sensors + computer + crew + ML. Since 1991 every major tank battle has been won by whoever sees and decides better.

If you want to feel the "detect + lock + fire" loop interactively, TANK//LOCK was designed around exactly that loop.