German U-Boat

Submerged attacks are more difficult but are necessary during daylight or attacks against warships. Underwater a U-boat is slow, un-maneuverable and almost blind. Enemy sonar and hydrophones could also detect a submerged U-boat. Due to its slow underwater speed, the U-boat had to be ahead of the convoy and already in a good attack position. Otherwise it may not be able to reach a favorable attacking position. Remaining concealed and undetected is vitally important, as once a U-boat is detected, the escorts will pursue it or the convoy will change course, leaving the U-boat far out of position.

U-boat ace, Erich Topp surveys the surface activity	A torpedoed merchant struggling to stay afloat in the Atlantic.

Once ahead of the convoy, the general approach is to dive deeper until the escorts have passed by. Depth reduces the effectiveness of sonar and through its hydrophones, the U-boat commander can locate the position of the escorts. To avoid detection, the U-boat has to move slowly in order to keep its engine noise low. This also helps conserve battery power. Once inside the convoy perimeter, the U-boat rises to periscope depth. Periscope observations are made in short peeks and at low speeds. Moving at low speed causes less periscope wake, helping to conceal the scope. If possible, the ideal direction of approach is with the sun towards its back. The glare makes it harder for enemy lookouts to spot the scope.

Once in position, the normal targeting procedure takes place. The largest targets are selected and a spread of torpedoes are fired, with the torpedo for furthest target being launched first. The commander is the only one who looked through the attack periscope and he alone made all targeting decisions. When a torpedo is launched, the weight of the boat had to be immediately balanced with ballast, as the launching of a torpedo caused more than a ton of positive buoyancy. If this was not offset by ballast, the boat could pop to the surface, giving away its position. Many U-boats were caught and abruptly attacked due to this simple error.

As soon as a torpedo was launched, the crew timed the torpedo’s run using a stopwatch. They waited and listened for the sound of an explosion at its estimated impact time, and if that did not happen, then it meant that the torpedo had missed its target.