End Around (submarine tactic)

An End Around was a World War II submarine attack tactic. It was used when the initial relative position of the submarine and its target did not give the attacking submarine a positional advantage. The submarine estimated the path and speed of the target, then submerged until the target was out of visual range. The submarine would then surface, and, remaining outside of visual range, proceeded at maximum surface speed to a position in front of the target. This position would give it sufficient positional advantage. The submarine would then submerge and wait until the target approached it before attacking.

Attack vector

This was an issue in submarine warfare prior to the development of nuclear powered submarines. Diesel electric powered submarines in the First and Second World Wars were typically capable of 15 knots on the surface under diesel power and 5 knots underwater using electric engines. As a result, they were generally slower than their targets. In order to position themselves for a torpedo attack a slower craft would have to approach from in front of the target.

The possible area in which the submarine had to make its approach varied according to the relative speed of the attacker and its target. In addition, the torpedo would have to strike the target at a sufficiently blunt angle to explode on impact, unless fitted with a proximity fuse, and also dependent upon the efficiency of the weapon. This angle is called the attack vector and consists of the number of degrees of arc on each side of the target’s course.

A convoy typically proceeded at 15 knots, which would provide an attack vector based upon a relatively wide area, but if the submarine was forced to submerge, the area of the attack vector would be drastically reduced.

Battle fleets in World War 2 would typically have a speed of about 30 knots (particularly if they contained aircraft carriers, as high speeds were necessary in order to launch aircraft). In World War 1, this was closer to 24 knots. Thus, these were difficult targets for submarines to attack in comparison to merchant ships. The attack vector would also be lost if the target detected the submarine and altered course.

Frequently, submarines would form patrol lines in order to await the approach of targets since they would otherwise be unable to pursue a quarry, especially in rough seas.

A nuclear submarine has a top speed in excess of 30 knots whether submerged or on the surface, enabling an attack vector of effectively 360 degrees against shipping of lesser speeds.