Area search torpedo
The German Navy of the Second World War called FAT a torpedo steered according to a mechanical process , which after a certain length of time alternately turned right and left and in between ran a predetermined distance straight ahead. The abbreviation stands either for area search torpedo or for spring apparatus torpedo .
The torpedo was adjusted to the target range as part of the calculation of a fire control solution. At the end of this distance, the torpedo went into FAT mode and after a set distance of 800 to 1900 m drove either an angle of 90 or 180 °. The direction of this initial turn (left or right) was also set. The torpedo then traveled the specified route again and at the end turned again, this time in the other direction. In this way, the course of an FA torpedo described characteristic "loops".
The FAT technology was primarily intended for submarine warfare to fight enemy convoys and closed units. In the event of a missed target, the torpedo should be held in this way within the convoy so that it may hit another target.
FATs were developed during 1942 after the importance of convoy attacks using pack tactics had risen sharply the previous year . Towards the end of the year the first FAT modifications of the types G7a and G7e were available, which were used regularly from the beginning of 1943.
The position-independent torpedo (LUT) represents an improvement of the FAT .