During World War I, the U-boat almost won the war for Germany. Karl Donitz had commanded a U-boat in World War I, and as the commander of the Kriegsmarine’s U-boat arm at the outbreak of World War II, determined he could do better the second time around. Though Hitler never gave him the promised time to build up the strength of the U-boat arm before the war began, Donitz very nearly came through with victory for his leader in the Battle of the Atlantic. Much of the reason that he didn’t came down to air power.

Losses mounted rapidly, and although aircraft joined the battle late, they sank U-boats at a much higher rate than escort vessels, accounting for almost half of the final total of U-boats sunk.

In contrast to the Battle of Midway, which lasted mere days, or the Battle of Britain, which lasted months, the Battle of the Atlantic went on from the first day of the war to the last. By war’s end, 30,000 Allied merchant seamen had gone down with more than 2,600 of their ships, along with 175 Allied naval vessels. Thousands of Royal Navy and U.S. Navy sailors, RAF and U.S. Navy and Fleet Air Arm aircrew were also lost, but the U-boat arm suffered grievously as well. Of the 40,000 German sailors aboard U-boats during the war, more than 28,000 died at sea, with 784 U-boats out of a total of 1,162 lost to all causes. Nevertheless, Great Britain was nearly strangled into submission, Churchill himself admitting that the U-boat threat was his greatest fear of the war.

The Royal Navy entered the war confident that ASDIC (Sonar) would defeat the U-boat, so much so that other preparations were overlooked. In fact, the U-boats were often faster on the surface than any pursuing escorts, and could attack at night with darkness to hide them. The answer to keeping the convoys safe was to keep the U-boats down, where they were slower than the convoys, which could then pass above them and out of range of pursuit. The solution to this problem was ASV radar aboard very long range aircraft, as well as organic air cover, but both of these were slow – too slow – in coming.

Air power served Donitz’ purposes in the Battle of the Atlantic as well, his Fw 200 Condors scoring many sinkings on their own, as well as shadowing convoys while they guided U-boats to them. Churchill referred to the Condors as “the scourge of the Atlantic,” and every effort was made to find solutions that would neutralize them. First among these was the CAM ship, equipped with a Hurricane or other fighter atop a catapult, to be launched upon the sighting of a Condor shadowing a convoy. CAM ships carried out eight fighter launches in 170 trips, and six Condors were shot down, though this was probably cold comfort to the pilots of the Hurricanes, who had to ditch their airplane at sea and hope to be rescued before freezing to death or drowning.

“Losses, even heavy losses, must be accepted if they are accompanied by proportional success in tonnage sunk,” wrote Donitz in his war diary. “But in May one U-boat was lost for every 10,000 GRT [gross registered tons] sunk. Thus our losses so far in May have reached an intolerable level. The enemy air force played a decisive role in inflicting these high losses.”

Escort carriers – either converted merchant ships with flight decks welded topside or purpose-built vessels – were a more workable solution, keeping Condors at bay and more importantly sinking U-boats or at least keeping them submerged, though flying off tiny decks in North Atlantic sea conditions caused a high rate of attrition. Later experiments with hunter-killer groups of escort carriers and anti-submarine vessels proved highly successful. Largely unheralded among naval aviators, the pilots and crew flying from escort carriers were an accomplished and hardy bunch, having to contend with the filthy weather and sea conditions of the Atlantic as well as the hazards of flying from very small carriers. The late Capt. Eric “Winkle” Brown, renowned naval aviator and test pilot, described his first escort carrier, HMS Audacity:

Of course, it was a difficult ship to fly from because the flight deck was only 420 feet long, which is extremely small, and the flight deck beam was only 60 feet, so you were flying from really a very small mini-carrier. The other thing I should say about it was: it only had two arrestor wires, so it required pretty accurate flying to get on. It had these two wires, but there was then a further wire immediately before the barrier.  We had a crash barrier in case you missed the wires, but if you caught this third wire (which was always named the “For Christ’s Sake” wire because if you went into this wire you were given very severe retardation which possibly could break the aircraft) if you did pull the wire out to most of its full length, the barrier then collapsed – they were interconnected, so the barrier collapsed and you ran over the barrier, so you could be saved by this third wire.

It had no aircraft hangar as such, so all the aircraft were up on the flight deck, and this made it a very tough business for the maintenance personnel who had to do everything on the flight deck.

The other key to victory was closing the “Air Gap” or Mid-Atlantic Gap between North America and Great Britain, the regions beyond the range of land-based aircraft, where U-boats could roam unmolested without fear of air attack, an area which the German sailors referred to as “The Black Pit.” Coastal Command, always the poor relation of the air arms in terms of equipment, nevertheless grew to the point that there were enough aircraft and crews to narrow the gap, and the arrival of very long range (VLR) Liberators nearly closed it completely. The lethality of these patrolling aircraft derived in part from the Leigh Light, essentially a stabilized searchlight, teamed with ASV (Air to Surface Vessel) radar to deny the U-boats the cover of darkness. Losses mounted rapidly, and although aircraft joined the battle late, they sank U-boats at a much higher rate than escort vessels, accounting for almost half of the final total of U-boats sunk.

By May 1943, the Battle of the Atlantic was essentially won. “Losses, even heavy losses, must be accepted if they are accompanied by proportional success in tonnage sunk,” wrote Donitz in his war diary. “But in May one U-boat was lost for every 10,000 GRT [gross registered tons] sunk. Thus our losses so far in May have reached an intolerable level. The enemy air force played a decisive role in inflicting these high losses.”
Though the Battle of the Atlantic would continue to the bitter end, the imbalance of German losses to sinkings would never recover, and the Battle of the Atlantic made the ultimate victory over Nazi Germany possible.