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Anti-ship missiles have been, since 1967, a deadly threat to surface warships.  Vast sums of money have been spent on guided missile systems, and electronic countermeasures to defeat them. Indeed, the entire impetus behind the Aegis radar/combat management system of US cruisers and destroyers was defense against anti-ship missiles.

But one of the most effective defenses against anti-ship missiles is also one of the cheapest.

Chaff.

Most anti-ship missiles use an active radar seeker for terminal guidance. Radar, of course, works by reflecting radio frequency energy off a target, back to the seeker.

Chaff disrupts this by placing thousands of tiny slivers of metal in the air, and thus generating enormous radar returns to obscure the real target. Think of it as a smoke screen for radar. While the first iteration of chaff in World War II was strips of metallic foil, today it is usually slivers of fiberglass or mylar with a metallic coating. And the length of each sliver is tuned to the likely wavelength of a radar seeker for an anti-ship missile.

To get the chaff into the air, a surface warship uses a special type of mortar. In the US Navy, that’s the Mk 36 Super Rapid Blooming Offboard Chaff launcher, or SRBOC.

In a typical scenario involving a US destroyer, an incoming anti-ship missile would likely be detected by either the ship’s SPY-1D radar, or by the ship’s SLQ-32 Electronic Countermeasures set picking up the missile’s seeker or radar altimeter.

The destroyer might try engaging the missile with its own SM-2 Standard Missiles, or the Evolved Sea Sparrow Missiles. It might also use active jamming from the SLQ-32. It will also likely use the Nulka active decoy countermeasure. And the ship will almost certainly use SRBOC.

A review of all known anti-ship missile engagements show that simply using chaff has been remarkably effective in defeating anti-ship missiles.

The recent Iranian backed Houti rebels firing on USS Mason last month reiterate the value of this most basic self defense capability.