The Mid-Atlantic gap is a geographical term applied to an undefended area beyond the reach of land-based RAF Coastal Command antisubmarine (A/S) aircraft during the Battle of the Atlantic in the Second World War. It is frequently known as The Black Pit, as well as the Atlantic Gap, Air Gap, Greenland Gap, or just "the Gap". This resulted in heavy merchant shipping losses to U-boats. 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. History RAF Coastal Command, when it was created in 1936, was given responsibility for A/S (or ASW, anti submarine warfare) patrol. It was equipped only with small numbers of short-ranged aircraft, the most common being the Avro Anson (which was obsolescent by the start of World War II) and Vickers Vildebeest (which was obsolete); for a time, shortages of aircraft were so severe, "scarecrow patrols" using Tiger Moths were even employed. Bomber Command routinely got higher priority for the best, longest-ranged aircraft. Only as Bomber Command transitioned to four-engined aircraft did Coastal Command receive the castoffs, such as Vickers Wellingtons, which finally had adequate range for A/S patrol. Moreover, Coastal Command's motley assortment of Ansons, Whitleys, and Hampdens were unable to carry the standard 450 lb (205 kg) depth charge; that needed Wellingtons or Sunderlands. (The other aircraft capable of carrying it, the Avro Lancaster, was Bomber Command's crown jewel.) Coastal Command's prize was the Consolidated Aircraft Liberator GR.I, commonly called the VLR Liberator or just VLR. The Liberator B.I proved too vulnerable for bombing missions over Europe, but had excellent range and payload, ideal for A/S patrol. Top priority for these was the U.S. Navy for reconnaissance operations in the Pacific, where their long legs were equally valuable, but where they generally carried out missions of lower priority than Coastal Command's. VLRs were of particular importance in times when Bletchley Park was unable to read Kriegsmarine Enigma (Ultra). When ON 127 was attacked by on 11 September 1942, there was exactly one VLR of 120 Squadron overhead. Fifteen U-boats converged on ON 131, only to meet aircraft, and Coastal Command sank two, while in protecting ON 136, 120 Squadron's VLRs sank on 12 October 1942. Even then, VLRs proved invaluable in co-operation with shipborne "Huff Duff". Defending SC 104, VLRs guided by HF/DF drove off