Looking at the vast expense of radars and missiles and even guns that equip naval ships for protection against anti-ship missiles, you might be forgiven for not realizing that only a handful of ASMs have ever even been engaged by shipboard missiles, and that by far, the most effective means of missile defense at sea has historically been passive defensive measures such as chaff.
One deception measure is the “rubber ducky.”
Given the choice of two radar returns, generally the seeker logic of an anti-ship missile will chose the larger of the two. Now, here’s the secret- the size of a radar return has no real correlation to the size of the object reflecting the radar energy. The amount of radar return generated is far more a function of the shape of the object. And so, the SLQ-49 Rubber Ducky allows a surface ship to quickly send overboard a pair of inflatable radar reflective floats that are tethered together.
The system is entirely passive. Which makes it cheap, very reliable.
Inside the little floaty thingies, by choice of shaping, materials, and careful calculation of anticipated wavelength of the seekers (and making length of reflective surfaces a multiple (or fraction) of that wavelength, the RF energy reflected can be much greater than the mere size of the floats would lead you to suspect.
The SLQ-49 was fielded in 1985, which means it was in development for some time before. You know what else was developed and fielded at roughly the same time frame? The F-117 stealth fighter. But instead of using shaping, materials and facets to reduce the radar signature, the Rubber Ducky embraced a sort of stealth in reverse.