Mid-Atlantic gap
The gap was eventually closed in May 1943, as growing numbers of VLR Liberators (Very Long Range models) and escort carriers became available, and as basing problems were addressed.
[3] Moreover, Coastal Command's motley assortment of Ansons, Whitleys, and Hampdens were unable to carry the standard 450-pound (200 kg) depth charge; that needed Wellingtons or Sunderlands.
[12] "...[T]he apparent inadequacy Newfoundland-based air support was highlighted by the early interception of SC 107 and the resultant bitter and costly battle.
The nine Liberator GR.Is operating over the Atlantic,[4] members of 120 Squadron based in Iceland, were nevertheless a worry to Admiral Karl Dönitz, who was Befehlshaber der U-Boote.
[21] Despite a willingness of Royal Canadian Air Force (RCAF) aircraft to fly in (perennially bad) conditions off the Grand Banks Coastal Command would never have attempted,[22] U-boats could trail convoys beginning very soon after departure from Halifax.
[23] Without air-to-surface-vessel (ASV) radar, the almost "perpetual fog of the Grand Banks also allowed pack operations to penetrate within a couple of hundred miles of Newfoundland, while aircraft patrolled harmlessly above",[24] and made visual detection impossible.
A means of detecting surfaced submarines at night, when they were at their most vulnerable, recharging batteries, and felt most safe, was a top priority for Coastal Command.
[3] ASV.II's 1½-metre wavelength (actually 1.7 m, 176 MHz),[25] mid-VHF band emissions meant however, that a submarine was usually lost in sea return before it came in visual range,[24] at around one mile (1.6 km), by which time it was already diving.
[29] Harris made similar objections to supplying the American-created 3 cm-wavelength H2X radar units to Coastal Command (which knew it as ASV.IV),[30] again got higher priority, and again saw it fall into German hands, almost exactly a year later, in February 1944.
ASV.III made its first U-boat contact on the night of 17 March, but the carrier Wellington suffered a malfunction of its Leigh Light and was unable to press home the attack.
[26] When ASV.III did enter service, German submariners, right up to Dönitz, began to mistakenly believe British aircraft were homing on emissions from the Metox receiver,[26][32] which no longer gave warning.
Naxos was replaced by FuMB36[34] Tunis in May 1944,[31] and was supplemented by Stumpf, what today would be called radar absorbent material, under the codename Schornsteinfeger ("Chimneysweep").
King got control of A/S aircraft from the United States Army Air Forces (USAAF), arranging a trade of B-24s for comparable types.
[39] The arrival of 25th Antisubmarine Wing, USAAF, with its medium-range B-24s (equipped with H2S, probably built by Canadians),[40] made it possible to free up Coastal Command VLRs without it.
After a crisis in March which nearly had Churchill and the Admiralty abandon convoys altogether,[42] the Mid-Atlantic Gap was finally closed in May 1943, when RCAF VLRs became operational in Newfoundland,[43] by which time the Battle of the Atlantic was largely won.
