This diagram appeared in Atlantic Convoy Instructions, a manual issued to convoy escort commanders during World War 2. Specifically, it comes from Article 106, detailing the Beta Search maneuver, which was used by British warships to defend merchant convoys from German submarine attacks. This image was digitally cleaned to remove blemishes and scribbles.
GENERAL IDEA
7. A U-Boat is sighted on the surface. In order to persuade the U-Boat to steer in a definite direction, course is not altered directly towards U-Boat on sighting.
The Officer of the Watch must note the time, bearing and estimated range.
EXECTION
(a) If the escort sights the U-Boat on a bearing 30 degrees on the bow, alter course towards the U-Boat but not directly towards, and increase to full speed.
If the escort sights the U-Boat fine on either bow, remain on that course, and increase to full speed.
If the escort sights the U-Boat right ahead, alter course at once before the U-Boat has time to dive, 20 degrees towards the rear of the convoy.
(NOTE that the U-Boat's last sighting of the escort is a fine silhouette. The U-Boat may seize the opportunity to increase his distance from the anticipated line of advance of the escort by steering a course at right angles to the escort, away from the escort's line of advance.)
(b) When the U-Boat has submerged, alter to the approach course (see paragraph 8)
(c) Reduce to asdic operating speed (applicable to destroyers) when within one mile of the U-Boat's "furthest towards" circle.
(d) On reaching the U-Boat's anticipated line of escape, mark the position with a sea marker. Continue on the attacking course until at the U-Boat's "furtest away" circle.
(f) Then turn 90 degrees twoards the U-Boat's diving position and commence operation OBSERVANT.
(g) How long operation OBSERVANT is continued depends upon the initial diving range, and the time availabe.
(h) If more than one escort can participate, the second escort to arrive should either commence OBSERVANT immediately, or join up with it if the first escort has already started it.
NOTE.-"Furthest twoards" and "furthest away" circles should be drawn allowing for a U-Boat speed of 7 knots.
APPROACH COURSE
8. The approach course should be worked out to cover a move of the U-Boat at an average speed of 4 knots, at right angles to his bearing on diving away from the track of the escort vessel as last seen by the U-Boat.
- As example :—Bearing 270 degrees (by compass).
- Bearing on diving, Red 15 (relative).
- Ancitipated course of U-Boat, 180 degrees
For a corvette with a speed of 15 knots, the approach course is 15 degrees to the right or left of the bearing of the U-Boat on diving, irrespective of the range.
For a destroyer with a speed of approach of 20 knots until reducing to maximum sweeping speed, this angle is slightly less and varies with the range on sighting. It is reocmmended that the angle to alter is worked out beforehand for various ranges of sighting, and also for a higher speed of initial approach in the event of more speed being available.
