The Mid-Atlantic Air Gap
—Jason

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The Battle of the Atlantic is the longest continuous battle in World War II, starting 3 September 1939 and lasting until 8 May 1945.  The British and American navies struggled against the German Kriegsmarine.  Allied and Axis aircraft, surface warships, submarines, and merchant ships were the main combatants throughout the war. 

At the outbreak of World War II, the German Kriegsmarine lacked large numbers of battleships, cruisers, and destroyers which limited the Nazis ability to confront the British Royal Navy.  The Germans were forced to adopt a strategy that revolved around attacking the merchant ships that supplied the British.  Several sorties by German surface raiders took place early in the war, but Hitler limited those operations after the loss of the battleship Bismarck in May 1941.

While Germany did eventually build several battleships, the real threat to Allied naval control were the hundreds of U-boats that were continuously launched from German shipyards.  U-boats were submarines that could be deployed in the North Atlantic.  A unique variant of U-boat was the milch-cow, or milk-cow, which was a long-range resupply ship that could extend the range of other U-boats into the Caribbean Sea and South Atlantic.  By 1942, the U-boats were operating nearly everywhere in the Atlantic Ocean.

U-boats operated either as individuals or in large groups called wolfpacks that savaged Allied and neutral merchant ships.  A U-boat that spotted an enemy convoy radioed its position and then shadowed its prey.  U-boat Command in Europe would then send signals to other U-boats patrolling nearby to converge on the convoy.  Slowly, more and more U-boats would close on the merchant ships and launch their attacks either during the day or, much more preferred, at night. 

Despite the advantage of being able to attack both while submerged or on the surface, U-boats were still vulnerable to attack.  One of the dangers for U-boats occurred when they were on the surface recharging their batteries and getting fresh air.  Depending on how deep they were submerged, U-boats could even be spotted and attacked by patrolling aircraft.  The British and American navies expanded the number of long-range land-based aircraft to hunt for U-boats near the coastlines. 

One of the best areas for U-boats to hunt was in the Mid-Atlantic gap, a region of ocean stretching between North America and the British Isles roughly south of Greenland.  German-U-boats could run on the surface, where their speed was much greater than submerged, for extended periods of time without fear of air attack in the Mid-Atlantic gap.  Most Allied aircraft did not have the range to patrol this region, the exception being the B-24 Liberator heavy bomber.  The United States Army Air Corps consistently gained larger numbers of the B-24 due to their need for a strategic bomber to hit German targets in Europe.  The B-24 was only available to the British Royal Navy and United States Navy in limited numbers. 

The British, Canadians, and Americans split escort duty between their forces to ease the strain on the limited number of escorts available.  Canada, and along with the United States, would escort Allied merchant ships up to Greenland and the British Royal Navy would continue the escort to the British Isles.  This arrangement had been agreed upon in 1940, well in advance of the United States officially entering World War II.

The Allies also had a limited number of aircraft carriers available to them in the early to mid-years of the Battle of the Atlantic.  Large carriers were reserved for fleet actions and only on rare occasions where they were attached to convoys.  Most of the large fleet carriers in the United States Navy had been stationed in the Pacific Ocean to blunt the Japanese.  The British Royal Navy lacked smaller aircraft carriers to attach to the convoys.

Losses in the Mid-Atlantic gap approached catastrophic as more and more wolfpacks attacked the convoys leaving North America bound for Great Britain.  Although destroyers and frigates acted as escorts, there were never enough of them to protect against every avenue of attack.  If an Allied ship was damaged or sunk, the captains of the remaining ships had orders to continue sailing and not stop for rescue operations.  These Allied convoy routes were constantly under German attacks between 1940-1943.  A solution to this air gap was desperately needed and weighed heavily at Allied military conferences.

After the United States entered the war, its shipyards started to mass-produce a new type of warship: the escort carrier.  The escort carriers were merchant ships converted with a flightdeck that enabled them to carry several fighter and bomber aircraft.  Initially when their numbers were still limited, the escort carriers were assigned to operate within the convoys.  By 1944, most Atlantic convoys included at least one escort carrier providing air cover for the entirety of the voyage.

The industrial plants and shipyards were able to supply the Allies with an almost unlimited number of warships and aircraft.  By May 1943, B-24 Liberators were operating out of Great Britain, Greenland, Iceland, and Nova Scotia further hampering U-boat operations.  As more became available, the escort carriers grouped into what was termed “hunter-killer groups.”  The hunter-killer groups were comprised of carriers, destroyers, and smaller destroyer escorts.  Their mission involved operating independent of convoys and eliminating German U-boats.  They became so effective that German U-boats were no longer able to prowl the Mid-Atlantic gap on the surface.