Convoy ON 122

As western Atlantic coastal convoys brought an end to the second happy time, Admiral Karl Dönitz, the Befehlshaber der U-Boote (commander in chief of U-Boats), shifted focus to the mid-Atlantic to avoid aircraft patrols. Although convoy routing was less predictable in the mid-ocean, Dönitz anticipated that the increased numbers of U-boats being produced would be able to effectively search the area with the advantage of intelligence gained through B-Dienst decryption of British Naval Cypher Number 3.[5] However, of the 180 trans-Atlantic convoys sailing from the end of July 1942 until the end of April 1943, only 20 percent lost ships to U-boat attack.

The Norwegian-manned corvettes of Escort Group B6 fought three of these convoy battles in sequential voyages with convoys SC 104, ON 144, and HX 217.[6]

U-135 discovered and reported the convoy on 22 August while patrolling a formerly assigned station after having missed the signal to change position. The initial report caused some confusion because of the unexpected position and a coding error, but after U-135 sent two clarifying messages while shadowing the convoy, the wolf pack Lohs was ordered to converge on the convoy.[7]

While the Norwegian corvettes investigated HF/DF bearings provided by Viscount and Stockport on 23 August, Viscount conserved fuel by declining to engage in long daylight stern chases with U-boats. Viscount and Potentilla attacked HF/DF contacts more aggressively through the hours of darkness, but were satisfied by simply forcing the U-boats to submerge rather than conducting sustained depth charge attacks.[4]

Visibility was reduced to 7,000 yards with patchy squalls under overcast skies on 24 August. As dusk approached, the escort had located only four of the nine U-boats in contact with the convoy. The convoy's course was altered to 267°  at 2300Z. U-605 torpedoed Katvaldis and Sheaf Mount on the starboard side of the convoy an hour after the course alteration. Viscount obtained a RADAR contact and forced the submarine to submerge. As Viscount was dropping depth charges, U-176 and U-438 entered the front of the convoy to torpedo Trolla and Empire Breeze.[4]

The convoy escorts effectively intercepted attacks through the pre-dawn hours of 25 August. The calm sea conditions were favourable for the Type 271 centimeter-wavelength RADAR with which all the escorts were equipped, and prompt counter-attacks prevented the U-boats from reaching torpedo launch positions. A depth charge attack by Eglantine holed the conning tower of U-605.[1] U-135, U-174 and U-438 were also damaged by depth charges.[7] The shadowing U-boats lost contact after the convoy entered heavy fog after daybreak on 25 August, and discontinued pursuit on 26 August.[4] U-256 was under repair for more than a year after being bombed in the Bay of Biscay on 31 August following depth charge damage from Viscount and Potentilla. U-438 aided U-256 reaching port, and U-174 refueled three Lohs U-boats before returning to France to repair damage.[1] U-705 suffered several casualties when hit by gunfire from the convoy escorts; and was sunk in the Bay of Biscay by Armstrong Whitworth Whitleys of No. 77 Squadron RAF on 3 September.[7]

The ships in the convoy dispersed off Cape Cod on 3 September to proceed independently to North American ports.[2]

• Convoy Battles of World War II

• Blair, Clay (1996). Hitler's U-Boat War: The Hunters 1939–1942. Random House. ISBN 0-394-58839-8.
• Hague, Arnold (2000). The Allied Convoy System 1939–1945. Naval Institute Press. ISBN 1-55750-019-3.
• Milner, Marc (1985). North Atlantic Run. Naval Institute Press. ISBN 0-87021-450-0.
• Morison, Samuel Eliot (1975). History of United States Naval Operations in World War II, Volume I The Battle of the Atlantic 1939–1943. Little, Brown and Company.
• Rohwer, J.; Hummelchen, G. (1992). Chronology of the War at Sea 1939–1945. Naval Institute Press. ISBN 1-55750-105-X.
• Tarrant, V.E. (1989). The U-Boat Offensive 1914–1945. Arms and Armour. ISBN 1-85409-520-X.