Mid-Ocean Escort Force (MOEF) referred to the organisation of anti-submarine escorts for World War II trade convoys between Canada and Newfoundland, and the British Isles. The allocation of United States, British and Canadian escorts to these convoys reflected preferences of the United States upon United States' declaration of war and the organisation persisted through the winter of 1942–43 despite withdrawal of United States ships from the escort groups. By the summer of 1943, United States Atlantic escorts were focused on the faster CU convoys and the UG convoys between Chesapeake Bay and the Mediterranean Sea; and only British and Canadian escorts remained on the HX, SC and ON convoys.

Background On the basis of experience during World War I, the Admiralty instituted trade convoys in United Kingdom coastal waters from September 1939.Hague (2000) p. 23 Anti-submarine escorts were allocated on the basis of perceived threat. Early German Type II submarines from bases in Germany were unable to operate effectively beyond European coastal waters. Following acquisition of bases in Norway and France, German Type IX submarines and German Type VII submarines refuelled by German Type XIV submarines operated in the mid-Atlantic beyond the range of patrolling aircraft. Many anti-submarine escorts lacked the endurance to accompany convoys through the mid-Atlantic. HX 129 left Halifax on 27 May 1941 as the first convoy to receive escort for the entire trip.van der Vat (1988) p. 187 Escorts based in Halifax Harbour handed HX 129 off to escorts based in Newfoundland who subsequently transferred HX 129 to escorts based in Iceland who in turn delivered HX 129 to escorts based in the Western Approaches.

American escorts

In Newfoundland on 9 August 1941, President Franklin D. Roosevelt agreed to provide American destroyers for the Canada to Iceland portion of HX convoys and westbound ON convoys.van der Vat (1988) p. 205 HX 150 sailed 16 September 1941 as the first convoy with American escort.Morison (1975) p. 86 ON 18 sailed 24 September as the first westbound convoy with American escort.Morison (1975) p. 90 The Royal Canadian Navy continued to escort the SC convoys and their slower ON counterparts.van der Vat (1988) p. 208 Canadian escort groups were increased from a nominal strength of four ships to six – typically one Canadian River-class destroyer with five s.van der Vat (1988) p. 209

The was torpedoed while escorting Convoy SC 48 on 17 October 1941.Morison (1975) p. 93 Clemson-class destroyer was torpedoed and sunk on 31 October 1941 while escorting Convoy HX 156.Morison (1975) p. 94 When the United States declared war, American escort groups typically contained five destroyers, although six United States Coast Guard s were included within the pool of ships rotating in and out of these escort groups.Blair (1996) p. 448

Long-range escort organization As the United States Navy struggled to find enough destroyers to meet escort needs for both the Pacific and the vulnerable Atlantic coastal shipping, the shorter great-circle route from Newfoundland to the British Isles was considered as a means of eliminating meeting point delays and reducing the number of destroyers required for escort of convoys between Canada and the United Kingdom. Initial proposals by the United States on 24 January 1942 produced an agreement in early February for a mid-ocean escort force organisation of fourteen escort groups.Blair (1996) pp. 457–9 American-led escort groups were prefixed with the letter "A"; while "B" indicated British-led escort groups and "C" designated Canadian-led escort groups. Fifteen United States destroyers, fifteen Royal Navy destroyers and twelve Canadian destroyers were to provide the striking power of these escort groups while 52 British and 49 Canadian Flower-class corvettes were to perform the patrolling role. Approximately one-third of the theoretical MOEF escort group strength of three destroyers and seven corvettes was unavailable at any given time.Milner (1985) p. 109 Half of the unavailable ships needed storm or battle damage repairs,Middlebrook (1975) p. 40 and the remainder were undergoing normal refit and training.

Each MOEF escort group worked in a 33-day cycle allowing nine and one-half days with a westbound ON convoy, six days in St. John's, Newfoundland and Labrador, nine and one-half days with an eastbound HX or SC convoy, and eight days' refit in Derry.Blair (1998) p. 25 The shorter routing away from Iceland eliminated the need for most escorts to attempt maintenance in Iceland's poorly equipped Hvalfjörður anchorage; but the United States was required to maintain an additional force of five destroyers in Iceland to escort ships between trans-Atlantic convoys and United States military occupation bases. The Royal Navy continued to provide an eastern local escort force of naval trawlers in the Western Approaches while Canada continued to provide a western local escort force (WLEF) of corvettes, minesweepers, and short-range destroyers between Halifax Harbour and Newfoundland.van der Vat (1988) p. 262

Initial MOEF escort group composition

Escort Group A-1: and s , and with Flower-class corvettes , and Rohwer & Hummelchen (1992) p. 124 Escort Group A-2: Gleaves-class destroyer and USCG Treasury-class cutter with Flower-class corvettes , , , , and Escort Group A-3: Gleaves-class destroyer with USCG Treasury-class cutter and Flower-class corvettes , , and Escort Group A-4: Benson-class destroyer and Clemson-class destroyer with Flower-class corvettes Impulse, , , , and , and Escort Group A-5: Gleaves-class destroyer and with Flower-class corvettes , , and Escort Group B-1: H-class destroyer with Rockingham, V-class destroyer , and Flower-class corvettes , and

Escort Group B2: H-class destroyer with Town-class destroyer Leamington, V-class destroyer , and Flower-class corvettes , , and Escort Group B-3: H-class destroyer with Town-class destroyer Georgetown, B-class destroyer , and Flower-class corvettes and , Free French and Escort Group B-4: H-class destroyer with Town-class destroyer Roxborough, W-class destroyer , and Flower-class corvettes , and Escort Group B-5: H-class destroyer with Town-class destroyer Caldwell, V- and W-class destroyers and , and Flower-class corvettes , and

Escort Group C-1: Canadian River-class destroyer and Town-class destroyer St. Croix with Flower-class corvettes , , and Escort Group C-2: Canadian River-class destroyer with Town-class destroyer Broadway and Flower-class corvettes , , and Escort Group C-3: Canadian River-class destroyers and with Flower-class corvettes , , and Escort Group C-4: Canadian River-class destroyers and with Town-class destroyer St. Francis and Flower-class corvettes , , and

Shortage of destroyers

Corvettes had adequate endurance for MOEF assignments, but the fuel economy of destroyers was poor at the speeds that convoys operated. The escort group leaders were modern destroyers with adequate endurance but, of the older destroyers allocated to trade convoy escort, only the Clemson subgroup of the Town-class destroyers proved suitable for MOEF assignments.Milner (1985) p. 98 Wickes-class destroyers were useful for the Canadian WLEF and the American Iceland shuttle; but lacked endurance to stay with a trade convoy for the full distance covered by the MOEF Escort Groups. The Admiralty converted some V and W-class destroyers to long range escorts by removing the forward boiler and using the space for additional fuel tanks.Lenton & Colledge (1968) p. 79

Nineteen modern American destroyers left the Atlantic to escort the battleships , , , and and the aircraft carriers , , and to the Pacific.Blair (1996) pp. 750–1 The remaining American destroyers were diverted from MOEF assignments to troop convoys and in response to the U-boat's Second happy time off the American east coast.Blair (1996) p. 460 Escort Groups A-1 and A-2 were disbanded when their modern American destroyer leaders were assigned elsewhere. Escort Groups A-4 and A-5 were redesignated B6 and B7, respectively, when the Royal Navy assigned F-class destroyers and as leaders.Milner (1985) p. 99 Escort Group B5 was reassigned to Caribbean trade convoys in March 1942. Beginning in April, the following eleven groups escorted HX convoys, SC convoys and ON convoys through the winter of 1942–43:

Escort Group A-3

Convoy HX 185 was escorted without loss.Hague (2000) p. 128 Gleaves-class destroyer Gleaves left the escort group after convoy ON 92 lost seven ships.Milner (1985) pp. 109, 113–6 USCG Treasury-class cutters Spencer and assumed escort leader responsibility. Flower-class corvettes Mayflower and replaced Flower-class corvettes Chilliwack, Shediac and Algoma.Milner (1985) pp. 290–1 Convoy HX 190 was escorted without loss. Convoy ON 102 lost one ship torpedoed by .Rohwer & Hummelchen (1992) p. 139 Convoys HX 196 and ON 114 were escorted without loss.Hague (2000) pp. 128, 158 Convoy SC 95 lost one ship torpedoed by .Rohwer & Hummelchen (1992) p. 157 Convoy ON 125 was escorted without loss.Hague (2000) p. 158 Flower-class corvette Rosthern joined the group. Convoy SC 100 lost three ships torpedoed by , and .Rohwer & Hummelchen (1992) p. 162 Convoys ON 135 and HX 212 were escorted without loss. Flower-class corvette Dianthus replaced Flower-class corvettes Mayflower and Bittersweet. Convoy ON 145 lost one ship torpedoed by .Rohwer & Hummelchen (1992) p. 167 Flower-class corvette rotated into the group. Convoys SC 111, ON 156 and HX 223 were escorted without loss.Hague (2000) pp. 128, 135 & 158 Convoy ON 166 lost eleven ships. Convoy SC 121 lost seven ships.Hague (2000) p. 135 Convoy ON 175 was escorted without loss. Convoy HX 233 lost one ship torpedoed by .Rohwer & Hummelchen (1992) p. 207 The escort group was then redesignated C-5 under Canadian command after the USCG Treasury-class cutters were reassigned for conversion to amphibious force flagships.Silverstone (1968) p. 373

Escort Group B-1 Flower-class corvettes , and joined the group; and Venomous was replaced by the long-range W-class escort .Rohwer & Hummelchen (1992) p. 227 Convoys HX 187, ON 96, HX 193, ON 108, SC 92, ON 119, HX 201, ON 124, HX 206, ON 134, SC 105, HX 215, ON 151, SC 114, ON 162, SC 119, ON 171 and HX 230 were escorted without loss. Convoy ON 178 lost three ships torpedoed by and .Rohwer & Hummelchen (1992) p. 206

Escort Group B-2

Flower-class corvettes , and Mignonette joined the group; and the low-endurance destroyers Leamington and Veteran were replaced by long-range V and W-class escorts and . Convoys SC 81, ON 97, SC 86, ON 107, HX 198, ON 118, HX 203, ON 128, HX 208, ON 138, HX 213, ON 148, HX 219 and ON 159 were escorted without loss. Convoy SC 118 lost eight ships. Convoys ON 170, SC 123 and ONS 4 were escorted without loss.Hague (2000) pp. 135, 159 & 163

Escort Group B-3 Low-endurance destroyers Georgetown and Bulldog were replaced by the E-class destroyer and the Polish destroyers and . Flower-class corvette replaced Heartsease and the four corvettes with Free French crews (Aconit, Lobelia, Renoncule and Roselys) were assigned to this group. Convoys HX 188, ON 98, HX 194, ON 110, SC 93, ON 121, HX 202, ON 126, HX 207, ON 136, SC 106, ON 146, HX 218, ON 157 and SC 117 were escorted without loss. Convoy ON 167 lost two ships. Convoy HX 228 lost four ships torpedoed by , and .Rohwer & Hummelchen (1992) p. 198 U-444 was rammed by the group leader Harvester. Harvester was then torpedoed by . U-432 was then sunk by Aconit. Thornycroft type leader was assigned as group leader replacement. Convoy ON 174 was escorted without loss.Hague (2000) p. 159 Convoy HX 232 lost three ships torpedoed by and .

Escort Group B-4