This was a British naval tactic devised by Captain F. J. Walker, commander of the 2nd Escort Group, for the sinking of U-boats (1942/45).
The tactic was based on the use of several warships. As one of these monitored the movement of a submerged U-boat from a distance too great for the U-boat captain to consider the warship a short-term threat. The stand-off warship then directed two other warships to approach the U-boat’s position very slowly and therefore very quietly within the use of their own sonar equipments, and thereby escape detection by the U-boat’s own hydrophone equipment. As the two 'creeper' warships reached the U-boat’s position, the stand-off warship signalled them to drop their depth charge patterns, which would detonate round the unsuspecting U-boat without a good chance of securing a kill.