EagleSpeak

An "interesting" idea from Ford. More on it here:

SCAT was a mechanical noisemaker affixed to large magnets which, when it attached to the hull of a moving submarine, generated noise that allowed the sub to be easily tracked. The SCAT was to be delivered using the already existing Hedgehog system. SCAT was the brainchild of inventor Frank Dobson, who also patented and developed a hovercraft and aircraft as well as children's toys. It's unclear exactly what the fate of the system was, but apparently it was never deployed, most likely because the odds of having the device successfully attach to the hull of a moving submarine at sea were very low.