In his history, The Second World War, British Prime Minister Sir Winston Churchill wrote: “The only thing that ever really frightened me during the war was the U-boat peril.” And well it might. For the second time in a generation, Germany’s Unterseeboote threatened to sever the North Atlantic lifeline that connected the New World with the Old.
The havoc wrought by the second German undersea offensive took the Royal Navy—and, indeed, every other navy—by surprise. Between the wars naval opinion had largely discounted the submarine as an instrument of war on trade. After all, the introduction of convoy had defeated the Kaiser’s U-boats in 1917. Since then, the invention of an underwater sounding device Britain named ASDIC (after World War I’s Allied Submarine Detection Investigation Committee) and the United States called sonar enabled surface vessels to locate submerged submarines at ranges up to 1,500 yards. If the Royal Navy had been able to confine the raiders’ depredations to acceptable levels before the appearance of ASDIC, it should certainly be able to do so afterward.
British overconfidence was reinforced by the fact that the new submarine threat was slow to materialize. In the late 1930s the German Navy had undertaken an ambitious expansion program, Plan Z, designed to create a formidable, balanced fleet—including 230 U-boats—by 1945. The commencement of hostilities in September 1939 nipped this buildup in the bud. By that date, then-Commodore Karl Donitz, Chief of U-boats, had 57 boats in commission and only 39 available for Atlantic operations.
Donitz appealed to the navy’s commander-in-chief, Grand Admiral Erich Raeder, to initiate a crash program to produce the 300 boats with which Donitz believed he could establish an effective blockade of the British Isles. Adolf Hitler readily approved Raeder’s recommendation; but not until July 1940 did he assign U-boat construction the priority in resource allocation necessary to implement his decision. Thereafter, the strength of the U-Waffe increased rapidly, from 49 boats in May 1940 to 420 by May 1943. The effect of its operations also followed an ascending curve, from 69,826 tons of Atlantic sinkings in March 1940 to 509,829 tons in March 1943.
In more remote ocean areas, U-boats still hunted singly, as they had in World War I, but the successes they won in the crucial North Atlantic convoy battles from 1941 to 1943 were the result of employing the Rndeltaktik—wolf- pack tactics—made possible by interwar advances in radio communications. Now the first boat to sight a convoy would shadow it, radioing reports that allowed Donitz, directing operations from headquarters ashore, to concentrate every boat in the vicinity into a pack in the convoy’s path. Then the wolves would attack, by preference at night and on the surface, the advantages of which included the neutralization of ASDIC. All too often, the convoys’ outnumbered escorts were swamped.
The courage and hardihood with which the men on both sides waged the struggle made its outcome dependent on an ongoing competition in intelligence, production, tactics, and technology. Among the Allies’ ingredients for eventual victory, the work of British codebreakers at Bletchley Park in penetrating the German Navy’s Enigma transmissions was extremely important; but other developments also played vital roles. These included the use of high-frequency direction-finding to locate U-boats sending radio signals; the assignment of more long-range aircraft to antisubmarine patrols; the invention of a forward-throwing depth-charge launcher called Hedgehog; the equipping of escort vessels with surface-search radar, while U-boats made do with radar-search receivers; the creation in March 1943 of escort groups that could be rushed to aid ocean escorts of hard-pressed convoys; and, later in 1943, the deployment of growing numbers of escort carriers in both convoy escorts and U.S. hunter-killer groups.
The fact that the balance had tipped decisively in the escorts’ favor first became evident in the battle of Convoy ONS-5. (ONS designated convoys from the United Kingdom to Sydney, Nova Scotia.) A very slow convoy of 42 merchantmen—most well past their prime—ONS-5 cleared the North Channel on 22 April 1943. Accompanying the convoy were two destroyers, a frigate, and four corvettes under Commander Peter Gretton, Royal Navy, an experienced escort leader in the destroyer Duncan.
Aside from the onset of gales that became its almost constant companion, the convoy’s early days at sea were generally uneventful, although on 24 April a Flying Fortress from Royal Air Force Coastal Command sank a U-boat in its path. On 28 April, however, the U-650 sighted the convoy and began broadcasting contact reports. The interception of these signals led Gretton to anticipate a busy night. He was not disappointed. After dark, the 15 boats assembled by the U-650’s transmissions made six attacks on ONS-5. Gretton’s ships beat them off without loss, damaging two U-boats in process; but after daybreak the U-258 slipped through his screen and sank a merchantman. Also on the 29th, Admiral Sir Max Horton, Commander-in-Chief, Western Approaches—who conducted the British side of the Atlantic battle—ordered the 3rd Escort Group from St. John’s, Newfoundland, to reinforce the convoy’s defenders. By the time the last of its five destroyers joined the convoy on 2 May, the onset of really vicious weather had brought the action to an end, scattering merchant vessels hither and yon and forcing the U- boats to stay submerged. That same day, Donitz instructed his wolfpack to give up the chase, and the Duncan and three other destroyers were obliged to proceed to Newfoundland to refuel. Gretton transferred command to Lieutenant Commander R. E. Sherwood, Royal Naval Reserve, in the frigate Tay.
But the convoy’s tribulations were far from over. On 4 May it blundered into a patrol line of 30 U-boats that Donitz had formed to intercept another convoy; an additional 11 boats were nearby. By this time, ONS-5’s main body consisted of 32 merchantmen screened by six escorts, while astern, the corvette Pink shepherded four stragglers. Once again, the volume of German radio traffic indicated that a major action was taking shape. Horton reacted by ordering the 1st Escort Group—a sloop, three frigates, and an ex-U.S. Coast Guard cutter—to sea from St. John’s. Weather conditions prevented land-based aircraft from reaching the convoy, but a Royal Canadian Air Force patrol plane sank the U-630 ahead of it.
Donitz considered the situation ideal, and the results of the night battle of 4-5 May seemed to confirm his opinion. Six merchant ships were sunk, and, although the escorts frustrated several other attacks, they did not destroy a single raider. During the daylight hours of 5 May, the plucky Pink killed the U-192, but submerged attacks claimed one of her little flock and four merchantmen in the main body. As sunset signaled the commencement of a second night action, the 3rd Escort Group’s commander reckoned that “the convoy faced annihilation.”
The ensuing encounter was indeed a fierce one; but this time it went in the convoy’s favor. Surfacing to make their torpedo runs, the U-boats found themselves groping blindly in a dense fog, unaware that the escort vessels were pinpointing their positions with radar operating on a wavelength the U-Waffe’s search receivers could not pick up. By British count, no fewer than 25 attacks were stemmed, four with fatal consequences to the attackers. One of Sherwood’s corvettes, the Loosestrife, accounted for the U-638; the destroyer Vidette’s hedgehog ended the career of the U-125; the U-531 was shelled by the corvette Snowflake and rammed by the destroyer Oribi; and the sloop Pelican, leading the 1st Escort Group into the fray, closed the books on the U-438 shortly before the action ended at 0420 on 6 May. Not one merchant vessel had been lost. Altogether, the 60 U-boats involved in operations against ONS-5 had sunk 12 merchantmen while losing seven of their own number. This represented an exchange rate of 1.7 to 1, a rate the U-Waffe could not endure.
Four other actions later in the month confirmed that the battle of Convoy ONS-5 had not been an anomaly. During the passage of HX-237, three U-boats were sunk in exchange for three merchantmen. The battles for SC-129, SC-130, and HX-239 each saw three boats—but not a single merchant ship—destroyed. For the wolfpacks to continue to take such unprofitable punishment would have been senseless, and on 24 May, Donitz withdrew them from the North Atlantic. In the war diary entry recording this decision, he expressed the conviction that it would be possible to resume the struggle once the boats received better antiaircraft armament; but when he attempted to do so in September, the results proved equally disastrous. With the benefit of hindsight, he drew the correct conclusion in his memoirs, ending his account of the events of May 1943 with the words:
“We had lost the Battle of the Atlantic.”
For further reading: Grand Admiral Karl Donitz, Memoirs: Ten Years and Twenty Days (Cleveland, OH: World Publishing Company, 1959); Vice Admiral Sir Peter Gretton, Crisis Convoy: The Story of HX231 (Annapolis, MD: Naval Institute Press, 1974); Captain S. W. Roskill, The War at Sea, 1939-1945, Volume II: The Period of Balance (London: Her Majesty’s Stationery Office, 1956); V. E. Tarrant, The U-Boat Offensive, 1914-1945 (Annapolis, MD: Naval Institute Press, 1989).