Convoy ON 166

A depth charge being loaded onto a depth-charge thrower aboard the corvette HMS Dianthus

Date	20–25 February 1943
Location	North Atlantic
Result	German tactical victory

Belligerents

United Kingdom

United States

Canada

Poland

Germany

Commanders and leaders

CAPT W E B Magee RN
CAPT P.R. Heineman USN

Admiral Karl Dönitz

Strength

63 freighters
1 destroyer
2 cutters
5 corvettes

18 submarines

Casualties and losses

14 freighters sunk (87,994 GRT)
262 killed/drowned

3 submarines sunk
128 killed/drowned
11 captured

Convoy ON 166 was the 166th of the numbered ON series of merchant ship convoys Outbound from the British Isles to North America. Sixty-three ships departed Liverpool 11 February 1943 and were met the following day by Mid-Ocean Escort Force Group A-3 consisting of the Treasury-class cutters Campbell and Spencer and the Flower-class corvettes Dianthus, Chilliwack, Rosthern, Trillium and Dauphin.

As western Atlantic coastal convoys brought an end to the second happy time, Admiral Karl Dönitz, the Befehlshaber der U-Boote (BdU) or 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 for convoys with the advantage of intelligence gained through B-Dienst decryption of British Naval Cypher Number 3. However, only 20 percent of the 180 trans-Atlantic convoys sailing from the end of July 1942 until the end of April 1943 lost ships to U-boat attack.

On 20 February U-604 sighted the convoy scattered by sailing eight days in a northwesterly gale. U-332 torpedoed the straggling Norwegian Stigstad on the morning of 21 February. U-623 was sunk by a No. 120 Squadron RAF B-24 Liberator that afternoon, and Campbell attacked a U-boat that evening. Postwar analysis concluded that Campbell sank U-225, but more recent re-evaluation indicates the attack may have destroyed U-529.

...
Wikipedia