The U.S. Navy submarine USS Tang off the Mare Island Navy Yard, California, December 1943. Photo credit: U.S. Navy
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Throughout the Second World War, American submarines were plagued by a variety of torpedo problems such as premature detonation and incorrect depth gauge. The most notorious of these was the tendency to circle back on the firing submarine. This is known as circular run.
Early torpedoes were only straight-running, like bullets fired from a gun, but in the early 20th century before the First World War broke out, torpedoes gained the ability to correct their course towards the target even if fired at a different direction. This correction angle, known as the torpedo's gyro angle, would be set mechanically while the torpedo was still in the tube. After the torpedo was fired, it would travel on a straight course for a short distance called the “reach”. Then the torpedo's gyro steering mechanism would kick in and the torpedo would start turning. After the desired bearing was reached, the torpedo would straighten its course and run towards the target.
Source: amusingplanet.com