'Plaster' (ii) was a British naval tactic developed by Captain F. J. Walker, commander of the 2^nd Support Group, to prevent a U-boat from evading an attack in the time between the fading of its sonar echo and the detonation of the first depth charges descending toward it (1942/45).

The tactic was based on the advance of three warships, in line abreast and at a speed of 5 kt, for the dropping of depth charges at five-second intervals to create a massive pattern of detonating in an area to large for the U-boat to make a complete escape. Proving that the depth charges were fused to detonate close enough the the target boat’s actual depth, the probability of sinking the target were high, although the cost in depth charges were very considerable.