Convoy ON(S)122 to Halifax and New York

17 August 1942 Outward bound North (Slow) 122 is the name of the convoy that left England at August 15th and by now has sailed clear from the English coast on the way to Halifax (Nova Scotia) and New York. ‘Slow’ means that its speed is in between 6-9 knots depending on the speed of the slowest ship. This route is also used by ‘fast’ convoys, average speed between 9-13 knots. Ships sailing faster than 13 knots are not only seen to be safer on their own instead of in a slower convoy but also to transport goods faster and more efficient because they don’t have to wait for a convoy and are not restricted by convoy routes. By 1942 statistics had proved  independent sailing ships had twice as much chance to be torpedoed opposed to those in a convoy. The minimum speed for sailing independent was raised to 15 knots but that didn’t improve the odds by much.

Convoy ON(S)122 consists of 36 merchant navy ships and an escort of 4 corvettes, 1 destroyer and 1 rescue ship. The convoy assembled August 15th 1942 and sets course to Halifax ( Nova Scotia) speed approximately 7 knots. The Germans are aware of the convoy and put a line of no less than 13 U-boats at a right angle to the probable course the convoy will take. Over the next few days This wolfpack named ‘Lohs‘ and ON(S)122 will be engaged in one of the larger convoy battles of the war. One of the 13 U-boats of this wolfpack is U-604.

Rescueship in ONS122 is SS Stockport with a HF/DF antenna. Stockport would be sunk with all hands by U-604 in 1943
(Source: http://www.wlb-stuttgart.de/)

To be able to carry out a Wolfpack attack the U-boats are in frequent radio contact with their headquarters in France. There the attack is coordinated. The Germans are unaware of the fact that the English can (partially) decode their messages and that the English escort ship are increasingly equipped with a device capable to detect the direction from which messages are sent the HF/DF (High Frequency Direction Finder of HuffDuff).

They use this on land and sea in different locations and, through triangular measurement, are able to locate the the U-boat sending the message and to reroute the convoy. ON(S)122 is swiftly rerouted the moment the English notice a wolfpack being formed on the planned route.
Unfortunately U-135 makes a mistake translating the instructions and places itself unknowingly on the new set course of the convoy.

Convoy ON(S)122

Pdt marks the position: 64 means 6th line 4th column. This convoy is 10 rows wide and 4 columns long. 
See also: warsailers.com.  Source of this overview: www.convoyweb.org.uk

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