"The "Fritz X" (or PC 1400 X) was a 3,450 lb. armor-piercing bomb fitted with a radio receiver and control surfaces in the tail. It was intended for use against heavily armored ships or ground targets. When dropped from 20,000 feet, an altitude above the most effective anti-aircraft defense, it could penetrate about 28 inches of armor. Aided by flares in the bomb's tail, the bombardier could follow its fall after release and could send radio signals which moved the control surfaces and produced minor changes in the bomb's course.
Later operational Fritz X bombs were wire-guided instead of radio-controlled to prevent jamming. The first operational use was on August 29, 1943--over the Mediterranean--and the most famous employment of the Fritz X was the sinking of the Italian Battleship Roma off Sardinia on September 9, 1943, to prevent its surrender to the Allies. Between April 1943 and December 1944, about 1,386 of these weapons were produced; 602 were expended in testing and training. Its combat use was limited by the small number of Luftwaffe aircraft available to carry it and its relatively poor accuracy, which averaged about 20% against Allied shipping."
From http://www.wpafb.af.mil/museum/annex/an41a.htm
