25 tracers a second: building the carrier point defence

Published 23 Oct 2026 · Updated 27 Oct 2026

A real Phalanx fires 4,500 rounds a minute from a 1,550-round magazine^[1]: about 20 seconds of fire. The carrier’s three point-defence mounts in Hostile Flagship fire 25 tracers a second from 500-round magazines. Each tracer stands for three real rounds; the 20 seconds of fire is real.

Three mounts

The carrier carries three medium mounts at Mk3: two on top of the stern engine pods and one under the belly. Their arcs and coverage are on the Phalanx page. At Mk3 they reach 1,250 m.

How a mount fires

It holds a track. Each mount re-picks its target 4 times a second, the way a fire-control radar keeps a track.
It picks the target it would hurt most: the enemy craft in range and inside its arcs that each round would do the most damage to, the nearer one only breaking a tie.
Just enough fire. It drops a target as soon as the rounds already in flight will finish it, and swings to the next. A turret facing a swarm keeps firing.
It leads. It aims where the target will be when the round arrives, from its position, speed and tracked acceleration, worked out in three passes because the flight time changes with the aim point. The acceleration is smoothed from tick to tick, as a radar’s filter would.
It fires only on target: within 1° of the lead point. Rounds leave at 1,100 m/s.

Every round is rolled

A hit is decided when the round is fired, by the shooter’s Mark against the target’s. The round then shows the result. A hit is steered onto its target and lands with a spark; a miss is sent a few metres to the side and flies on, the tracer streaking past. A real Phalanx watches its own rounds and walks them onto the target^[2]; the game rolls instead, and shows what the roll decided.

The landing check is swept, so a fast round can’t skip past its target between two ticks. Each round lives 2.3 seconds. Every mount uses a fixed random seed, so the same engagement plays out the same way twice.

Magazines and reloads

500 rounds a mount, about 20 seconds of fire.
Empty in a fight: a 5-second reload with the gun silent, then full.
Out of a fight, with nothing near for 3 seconds: topped up at once.
Rounds come from the light rounds in the carrier’s hold. It starts with 20,000, enough for 40 full reloads, shared with the fighters’ rearming.

Guns that hide in the hull

Each mount has three modes on the weapon bar: AUTO, OUT and IN.

In, a gun sinks into the hull under an iris cover. It can’t fire, and it can’t be shot.
Coming out or going in takes 1.5 seconds. A gun can fire, and be shot, from halfway out.
Auto, the default, brings it out when an enemy craft could be in reach by the time it is out, and puts it back 3 seconds after the last threat.

Keep a gun hidden as a trump card, or turtle up against a swarm that can’t scratch the hull. Each mount can be knocked out: a Mk3 turret has 120 hull.

Performance, then and now

The first point-defence build, on 23 October, fired 75 rounds a second from 1,550-round magazines and decided hits by the rounds’ paths. To keep it fast, rounds went into packed arrays and a spatial grid. On that early build, 90 mounts against 90 drones, with about 3,500 rounds in flight, cost 2.7 ms a frame on average. The same day, Combat v2 replaced path hits with rolled ones at 25 a second, and the grid went with it. The packed arrays, held tracks and swept landing check stayed. Today’s version has not been re-measured.

The reasons behind each number: point defence.

Why these numbers →

Sources

Phalanx CIWS, Wikipedia. The Block 1A and newer (pneumatic driven) CIWS mounts fire at a rate of 4,500 rounds per minute with a 1,550-round magazine.
Phalanx CIWS, Wikipedia. While firing 75 rounds per second, the system tracks outgoing rounds and 'walks' them onto the target.