Original U.S. Signals, Underwater Sound (SUS) MK 57 Dummy “Practice Depth Charge” - Inert

Item Description

Original Item: Only One Available. This is a wonderful example of a hard to find “Practice Depth Charge”, Mk 57 Signals, Underwater Sound Dummy device. This is an inert, practice device and was never intended to be used as an explosive device nor can it be used as such. It is in total compliance per the current BATF regulations governing ordnance.

Not Available For Export

The SUS is a small, expendable, bomb-shaped device 3 inches in diameter and 15 or 21 inches long (D and E size, respectively), with this one being 15 inches. The nose end is blunt. The body extends straight back from the nose and tapers to the tail; the tail fins are enclosed by a shroud ring. There are two basic types of SUS, one explosive and the other electronic. Launching enables the arming mechanism in the explosive type.

The explosive SUS generates sound by moving the water out with a large gas bubble. This bubble then collapses underwater pressure and compresses the gas, which then bounces back, re-expanding several times with diminishing force and time interval. The single explosion occurs at the SUS functioning depth. Water pressure, increasing as the SUS sinks, first arms the explosive train, then detonating the explosive charge. Spring loaded pistons and rupture (shear) discs are used to sense the water depth and to operate the arming and firing systems. The electronic type uses seawater as the electrolyte in the battery that powers the electronic circuitry, causing a coded sound to be projected into the water. The electronic circuit causes a ceramic ring to vibrate, creating sound waves in the water. This signal is transmitted for a short time as the SUS sinks.

This example is in wonderful condition and retains nearly all of the original blue dummy paint and extensive black stenciling are all components of the device. There is no extensive damage present but there is minor paint loss and we have not attempted to try an disassemble the SUS device to inspect the interior.

Comes more than ready for further research and display.

  • This product is not available for international shipping.
  • Not eligible for payment with Paypal or Amazon


Cash For Collectibles