Closing the Gap
Air Power and the Battle of the Atlantic
The Battle of the Atlantic is the longest continuous campaign in World War II, it ran from the first day of the war in 1939 to the defeat of Nazi Germany in 1945. At its core was the German commerce raiding of Allied merchant shipping. The Battle of the Atlantic pitted U-boats and other warships of the German Kriegsmarine (Navy) and aircraft of the Luftwaffe (Air Force) against Allied naval forces.
Treasury-class cutter USCGC Spencer was escorting Convoy HX 233 sailing from Newfoundland to Northern Ireland, April 1943. Spencer belonged to MOEF Group A3, she was responsible for sinking Type IXC U-Boat U-175 during this escort mission.
The Royal Naval Air Service invested heavily in aircraft of all types—airplanes, seaplanes, airships, and kite balloons—in order to counter the German U-boats in World War I. Despiting the challenges of organization, training, and production, the employment of aircraft against U-boats was largely successful during the Great War. After 20 years of development, air powers were ready to play a greater role in Anti-Submarine Warfare.
As an island country, the United Kingdom was highly dependent on imported goods. Britain required more than a million tons of imported material per week in order to survive and fight.
During that time period, the intercontinental-range strategic airlift still did not exist. Merchant shipping was the only way to transport heavy military equipment from the home front to the frontline. The allied merchant navy is the key to keeping frontline fighting in all theatres.
British passenger liner SS Athenia was sunken by U-30 on 3 September 1939, with 117 civilian passengers and crew killed, including 28 US citizens. It was the first British ship sunk by Germany in World War II and marked the beginning of the Battle of the Atlantic.
MAP: Allied air cover range for convoys from late 1939 to early 1940
Coastal Command was the RAF formation concentrated on anti-submarine and maritime patrol duties. Cooperating with RCAF Eastern Air Command, Coastal Command established ASW air cover covering the British and Canadian coast during the Phony War.
As the "Cinderella Service" in RAF, Coastal Command's air fleet lacked both quality and quantity. Their only advanced long-range maritime patrol aircraft was the Short Sunderland flying boat, and the Command only had 39 Sunderlands when the war outbreak.
A Short Sunderland Mk I flying boat of No. 210 Squadron RAF based at Oban in Scotland, patrols over Canadian Troop Convoy 6 on its way to Greenock, 31 July 1940.
It's even worse in RCAF Eastern Air Command, their only operational maritime patrol aircraft was Supermarine Stranraer, operated only by No. 5 Squadron RCAF when the war began. Thus, Canadians had to transform some Northrop Delta passenger transport aircraft to patrol floatplanes to carrying out the long ASW missions.
No. 5 Squadron RCAF's Supermarine Stranraer, produced by Canadian Vickers.
Until the fall of France on July 1940, the function of Coastal Command and its aircraft was to cover the English Channel, North Sea, and Western Approaches. Thus, Coastal Command's obsolescent or short-range aircraft, such as Avro Anson, Saro London, and Supermarine Stranraer, could still complete the ASW mission in the coastal area of UK and Canada.
During this time period, German submarines were not able to reach the Atlantic unless they undertook a dangerous transit journey through the North Sea and around Britain's northern waters or through the English Channel.
Things changed after the fall of France...
German commerce raiders gained direct access to the Atlantic by using naval bases in France at Brest, Lorient, Saint Nazaire, Bordeaux, and La Pallice & La Rochelle. These bases were also about 720 km closer to the Atlantic than the bases in German homeland. This greatly improved the situation for U-boats in the Atlantic, enabling them to attack convoys further west and letting them spend longer time on patrol, doubling the effective size of the U-boat force.
It caused the so-called "First Happy Time" (Die Glückliche Zeit). In the beginning stage, U-Boats sank nearly 300 Allied ships in only 5 months.
In September 21 1940, convoy HX 72 of 42 merchantmen was attacked by a pack of four U-boats, which sank 11 ships and damaged 2 over the course of two nights. In October, the slow convoy SC 7, with an escort of two sloops and two corvettes, was overwhelmed, losing 59% of its ships, including 20 sunk and 2 more damaged.
"The Wolf Pack Gathers: U-99, U-100, U-101 and U-123 Prepare to Attack Convoy SC7, 18 October 1940"
As a response, when Royal Navy enhancing its escort force, RAF established more air stations and delivered better aircrafts to its Coastal Command. These initiatives pushed the U-Boats to Mid-Atlantic, where has an area cannot be reached by Allied ASW aircraft. The area is called "Mid-Atlantic Gap".
MAP: Allied air cover range for convoys 1941
Short Sunderland Mk I of No. 204 Squadron RAF based at Reykjavik in Iceland, 1941.
After US declared war on Nazi Germany in the end of 1941, German Navy launched Operation Paukenschlag and Operation Neuland in 1942. U-Boats were sent to Americas to hit unprotected Allied and Pro-Allied merchant ships. Countries of the Americas include the US are not ready to fight U-Boats yet, Allies suffered significant losses from the East Coast to Caribbean. This time period is called "Second Happy Time" or "American Shooting Season" by U-Boats' crew.
US Tanker SS Pennsylvania Sun burning near Key West after being torpedoed amidships by U-571 on July 15 1942. She was traveling from Port Arthur to Belfast, with 107,500 barrels of Navy fuel oil.
By cooperating with Latin American countries, USN and USAAF established many new air stations in the Caribbean and South America. U-Boats were kicked out from "America's Backyard" and had to return to Mid-Atlantic once more in early 1943. Another Allies' major victory during this period was the operation of new air stations in Greenland and the arrival of more long-range ASW aircraft, including Consolidated B-24 Liberator, Handley Page Halifax, Boeing B-17 Flying Fortress, and Avro Lancaster. It led to the close of the Mid-Atlantic Gap's north side.
MAP: Allied air cover range for convoys 1943
USCG VPB-6 Squadron's PBY-5A Catalina at Narsarsuaq, Greenland, 1943. Today's Narsarsuaq Airport was the largest air base operated by Allies in Greenland, codenamed "Bluie West One", hosted USN squadrons of PBY Catalina flying boats and PBJ Mitchell bombers for ASW missions.
In early 1943, German submarine strength reached its peak, with about 240 operational U-boats, of which more than 100 were at sea. The U-boat offensive also reached its peak in March, with a series of major convoy battles that caused the Allies to lose 82 ships in the Atlantic. But the turning point appeared in May, U-Boat force suffered unprecedented losses in this month, 41 of them being destroyed by Allied forces. Relatively, Allies only lost 34 ships in May, and the initiative is no longer in the hand of the Kriegsmarine.
Air Marshal John Slessor was appointed Commander-in-Chief Coastal Command on 5 February 1943. He presented the plan for attacking the German vessels in the Bay of Biscay, in transit to the Atlantic. It led to a series of "Bay Offensive" in 1943. The result is contentious, although Coastal Command has successfully exerted pressure on the German submarine force, it also suffered significant losses over the Bay of Biscay because the bay was in the range of Luftwaffe's long-range fighters.
Type VIIC submarine U-243 attacked by Sunderland Mark III from No. 10 Squadron RAAF in the Bay of Biscay, 1944.
At the end of 1943, the British and American armed forces were allowed basing rights in Portugal. Portugal offered its Lajes Air Field in the Azores to the Allies, it helped Coastal Command to close the south side of the Mid-Atlantic Gap.
MAP: Allied air cover range for convoys 1944
Consolidated Liberator GR Mark VIs of No. 220 Squadron RAF parked at Lajes Field.
The initiatives and efforts the Allies made in 1943 led them to final victory. U-Boats were still a threat until the defeat of Nazi Germany, but they could not gain any strategic victory since 1943. After the Battle of Normandy, all German naval bases in France were abandoned, it marked the end of U-Boats' heyday.
German Type IXD2 U-boat, U-848, attacked by VB-107's PB4Y-1 Liberators near Ascension Island, 5 November 1943.
German Type IXC U-boat, U-515, attacked and sunk by USN's Edsall-class destroyer escorts and carrier-based aircrafts from VC-58 Squadron, 9 April 1944. It's an outstanding example of the Allied Air-Sea ASW collaboration.
There can be no denying that the destructive capability of air power was significant in taking a heavy toll on German submarines or U-Boats. By the end of hostilities in the European theatre, air power alone had accounted for 290 U-boats, compared to the 246 sunk by surface vessels. Of these 290, 245 were sunk by land-based aircraft, 195 being destroyed by the RAF, almost all by Coastal Command, with American units accounting for 48 (2 were shared). Moreover, aircraft aided in the destruction of another 48 U-boats in conjunction with surface units.
German Type IXC/40 U-boat, U-858, surrendered and took over by USN in the end of war, 14 May 1945.
"The only thing that ever really frightened me during the war was the U-boat peril."
By Winston Churchill
