Mid-Atlantic gap
In 1941, a black arc on the map marked the limit of safety for merchant ships crossing the Atlantic. Beyond this line lay an area where land-based aircraft could not reach. This region became known as the Mid-Atlantic gap. U-boats operated freely here, hunting Allied convoys without fear of aerial attack. The gap existed because no plane flying from Britain or North America had enough fuel to cover the distance and return safely. Ships sailing through this zone were effectively invisible to the sky above them. They relied solely on their own escorts and luck to survive. Many vessels fell victim to German submarines in these waters during the early years of the war.
RAF Coastal Command formed in 1936 with only small numbers of short-ranged aircraft. The most common planes included the Avro Anson and Vickers Vildebeest, both obsolete by the start of the Second World War. Severe shortages meant that scarecrow patrols using Tiger Moths were employed to fill gaps. These biplanes lacked any real capability against modern submarines. Only when Bomber Command converted to four-engined aircraft did Coastal Command receive castoffs like Vickers Wellington medium bombers. Even then, motley assortments of Ansons, Whitleys, and Hampdens could not carry standard depth charges. The situation remained dire until more capable aircraft arrived later in the conflict.
Coastal Command's prize was the Consolidated Aircraft Liberator GR.I, commonly called the VLR Liberator. This aircraft had excellent range and payload, ideal for anti-submarine warfare missions. Priority for these planes went initially to the U.S. Navy for reconnaissance operations in the Pacific. When Convoy ON 127 was attacked on the 11th of September 1942, one VLR from 120 Squadron flew overhead. Fifteen U-boats converged on Convoy ON 131 but met aircraft instead. Coastal Command sank two during this engagement. Protecting Convoy ON 136, the 120 Squadron VLRs sank another submarine on the 12th of October 1942. Despite their value, only nine Liberators operated over the Atlantic from Iceland by early 1943. Admiral Karl Dönitz worried about their presence near Canada. After patrols off Canada were added in 1942, only one ship was lost in convoy despite heavy attacks.
Detecting surfaced submarines at night became a top priority for Coastal Command. ASV radar systems provided initial detection capabilities but suffered limitations. The previous AI.II Mark 2 Airborne Interception radar became ASV.II fitted in Coastal Command aircraft. Its 1½-metre wavelength meant that a submarine was usually lost in sea return before visual range. By the time it came into view, the target had already dived. The Leigh light solved part of this problem when it entered service in June 1941. This device required large aircraft like the Wellington or Liberator to carry its generator. Most Coastal Command planes could not support such equipment. German forces developed Metox receivers which picked up ASV pulses before detection occurred. The appearance of H2S three gigahertz-frequency radar changed the dynamic entirely. Combined with the Leigh light, this system proved lethal to U-boats starting in late 1942.
Bomber Command routinely received higher priority for the best and longest-ranged aircraft available. Arthur Harris sought to have VLRs diverted from Coastal Command to attack German cities instead. Despite Professor Patrick Blackett's strong case, the Admiralty believed they could not afford to reduce air offensives over the Bay of Biscay. Marshal John Slessor countered that Bomber Command risked losing technology to enemy hands just as quickly. Winston Churchill backed Harris against Coastal Command demands. From the 14th of January to May 1943, Bomber Command flew 7,000 sorties against U-boat pens at Lorient, Brest, and St. Nazaire. They lost 266 aircraft and crews while accomplishing no damage to the pens themselves. Coastal Command strength never reached even a fraction of those numbers. This rivalry delayed critical improvements needed to close the Mid-Atlantic gap effectively.
A crisis in March nearly caused Churchill and the Admiralty to abandon convoils altogether. Increasing availability of escort carriers reduced the hazard significantly. By May 1943, the Mid-Atlantic gap was finally closed when RCAF VLRs became operational in Newfoundland. Thirty-eight VLRs covered the entire region by early spring. The arrival of 25th Antisubmarine Wing with medium-range B-24s freed up Coastal Command resources further. Canadians had been pressing hard for Liberators since autumn 1942 despite British doubts about their effectiveness. Squadron Leader Bulloch confirmed Royal Canadian Air Force capabilities during early March operations. The number of planes in Newfoundland doubled after attacks on convoy ONS 166. Twenty-five additional units joined the effort later that year. The Battle of the Atlantic was largely won by this point as losses dropped dramatically across all routes.
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Common questions
What was the Mid-Atlantic gap during World War II?
The Mid-Atlantic gap was an area outside airplane range in World War II where land-based aircraft could not reach. U-boats operated freely here, hunting Allied convoys without fear of aerial attack.
When did Coastal Command receive VLR Liberators to close the Mid-Atlantic gap?
Coastal Command received Consolidated Aircraft Liberator GR.I planes known as VLR Liberators starting in 1942. The Mid-Atlantic gap was finally closed by May 1943 when RCAF VLRs became operational in Newfoundland.
Why were early RAF Coastal Command aircraft ineffective against submarines?
Early RAF Coastal Command aircraft like the Avro Anson and Vickers Vildebeest were obsolete by the start of the Second World War. Severe shortages meant that scarecrow patrols using Tiger Moths lacked any real capability against modern submarines.
How did the Leigh light improve anti-submarine warfare capabilities?
The Leigh light entered service in June 1941 to solve detection problems for surfaced submarines at night. Combined with H2S three gigahertz-frequency radar, this system proved lethal to U-boats starting in late 1942.
Who prioritized Bomber Command over Coastal Command during the war?
Winston Churchill backed Arthur Harris who sought to have VLRs diverted from Coastal Command to attack German cities instead. Marshal John Slessor countered that Bomber Command risked losing technology to enemy hands just as quickly.