Mk 24 "FIDO" Air-Dropped ASW Homing Torpedo

   The primary aspect of U.S. World War II torpedo development, apart from copying electric torpedoes, was the design of a air-launched homing torpedo, fast enough  to catch a submerged submarine, yet slow enough to enable the torpedo to hear  the noise of a submarine over the flow noise created by itself. 12 knots was  thought to be perfect. 

    Work by General Electric, Harvard and Bell Laboratories, begun in 1941 led to the Mk 24 "mine", a designation maybe due to security necessities, which carried a 42kg Torpex charge, enough for the expected impact  detonation. The torpedo could run for up to fifteen minutes, yet most hits were  scored directly after the submarine's dive. 

    The main weapons carry within the Navy were the TBF Avenger and PBY Catalina, which employed the weapon in lieu of  and supporting depth charges. The first victim of the new weapon was U-467, sunk  by a plane of VP-84 in the Atlantic, May 25th, 1943. Following her would be 31  boats, with another 15 damaged. (Numbers for the U.S. Atlantic Fleet only, no figures found for Pacific drops. Likely none were executed. Weapon is included  for the sake of completeness and the possibility that it actually WAS used.).FIDO could be dropped at 125 knots from 250 feet. FIDO homed via four hydrophones and a simple steering mechanism pointing the torpedo toward the  source of the noise. 
    Typical mission profiles included forcing the submarine to dive, then drop the  torpedo onto its head. 

Year of Construction: 1942  
Bore: 483mm  
Weight: 308 kg / 680 lbs  
Length: 2134mm / 7ft 0in  
Range: 3660 m / 4000 yds at 12 knots  
Explosive Charge: 42 kg / 92 lbs Torpex