The Opening Convoy War

The convoy principle had been established in the First World War, and the Admiralty reintroduced it within days of the declaration of war. Regular east-coast convoys began on 6 September 1939 and outward ocean convoys on 7 September. The first Halifax convoy, HX 1, sailed on 16 September. The early arrangements were still incomplete. Escorts were scarce, ocean coverage was limited and many ships continued independently on routes that could not yet be protected continuously.

Convoy worked before the escorts became technically dominant because it changed the submarine's search problem. A U-boat could patrol an ocean route for days without seeing anything. Grouping dozens of ships into one moving formation reduced the number of targets at sea and allowed the available destroyers, sloops and armed vessels to protect several cargoes at once. The escort's task was to make the convoy harder to find, force the attacker to approach a defended formation and keep losses low enough that the cargo flow continued. By the end of 1939 the Royal Navy had escorted almost 5,800 merchant ships in convoy and lost twelve of them. In the same months 102 ships sailing independently were sunk.

The first months differ from the great North Atlantic convoy battles of 1941 to 1943. Germany had too few boats to maintain wide patrol lines for long. British escorts were often thin. Aircraft were better at finding submarines than destroying them, and much of the shipping loss occurred outside convoy. The machinery that later fought the decisive convoy battles was being assembled while the first campaign was already underway.

Karl Dönitz wanted U-boats to find convoys in patrol lines, report contact and concentrate other boats for a coordinated attack. The force available in September 1939 was not large enough to apply that method continuously. A British postwar study of German records counts 57 U-boats in existence at the outbreak and 49 ready for operational duties on 29 August. Only 18 were available for Atlantic operations on 7 September. Coastal boats, training requirements, maintenance and the long passage from German bases further reduced the number that could remain in the Western Approaches.

The attack of 17–18 October showed what Dönitz was trying to build. U-37, U-46 and U-48 were brought against convoy HG 3, sailing from Gibraltar to Liverpool, under central tactical direction. German records described it as the first attack of that type. The three boats sank three ships. It was evidence that concentration could work, but also evidence of the arithmetic problem. Werner Hartmann's group had started with six boats. One struck a mine on 13 October and two more were sunk in earlier attacks, so only three reached HG 3.

The force was then pulled in several directions. U-boats laid mines, attacked independent shipping and supported operations in the North Sea. In March 1940 they were withdrawn from the Western Approaches for the invasion of Norway. The Norwegian deployment produced many firing opportunities but exposed serious torpedo defects. When the boats returned to the Atlantic, the fall of France was about to solve a different German problem by bringing bases hundreds of miles closer to the convoy routes.

British destroyers and sloops entered the war with ASDIC, but the set was designed primarily to track a submerged submarine at relatively short range. A U-boat attacking on the surface at night could be difficult to detect. An escort that gained contact still had to manoeuvre over the target to deliver depth charges. The escort force itself was too small for the number of ocean, coastal and military commitments placed on it. Older destroyers therefore remained central to convoy defence while new Flower-class corvettes were only beginning to enter service in 1940.

Air patrols offered a way to search much larger areas. Coastal Command was assigned increasing responsibility for attacking U-boats as well as reporting them. The concept was ahead of the weapons. Crews had little specialised anti-submarine training. The 100-pound anti-submarine bomb proved useless against a diving U-boat, and in 1939 only the flying boats could carry the 450-pound depth charge. Aircraft could force a submarine under, break contact with a convoy and narrow the search, but the highly effective air-submarine combination belonged to a later stage of the campaign.

Mines created a separate threat to the same shipping system. German magnetic ground mines could block approaches without a submarine remaining in the area. On 21 November 1939 the cruiser HMS Belfast was mined in the Firth of Forth and put out of action for nearly three years. When a Type GA mine was recovered intact at Shoeburyness on 23 November, John Ouvry and the HMS Vernon team gave British scientists the firing mechanism they needed to design effective countermeasures. Degaussing and magnetic sweeps did not remove the mine threat at once, but they converted an unfamiliar weapon into a technical problem that could be attacked systematically.

Athenia, Courageous and Royal Oak made the opening months appear more disastrous than the convoy record alone suggests. A passenger liner was sunk on the first evening of the British war. A fleet carrier was lost while hunting submarines two weeks later. In October U-47 entered the Royal Navy's principal anchorage and sank a battleship. Each exposed a different vulnerability, and none of them broke Britain's Atlantic supply system.

Convoys were attacked and escorts were lost, but German boats found many of their easier targets outside the protected formations. At the same time the U-boat arm was paying a significant price. By the end of March 1940, between 17 and 19 German submarines had been lost, depending on whether accidents and losses in port are counted. Construction had not yet produced the large operational fleet Dönitz believed necessary for a sustained blockade.

By June 1940 both sides had shown what they could do. Britain had kept traffic moving with imperfect escorts. Germany had shown that submarines, mines and surprise attacks could impose serious losses. Norway interrupted the Atlantic offensive, and defective torpedoes wasted opportunities there. The defeat of France altered the strategic geography of the campaign. U-30 entered Lorient for refit on 7 July 1940, and the patrol route to the Atlantic was dramatically shortened.

The chronology is anchored in Stephen Roskill's official history and the Admiralty War Diaries for the British operational picture. The German side uses the translated BdU war logs and the postwar Admiralty history of German U-boat policy, which preserve the force numbers, convoy assessments and Dönitz's own reactions to the torpedo failures.

The Athenia and Royal Oak casualty figures are checked against Royal Navy and Imperial War Museums material. The magnetic-mine sequence uses the Admiralty history and the record of John Ouvry's recovery at Shoeburyness. Coastal Command's early limitations are taken from the RAF's official history and Bowhill's despatches. Sources give Athenia totals between 112 and 128, and the figure used here is 117. Counts of U-boat losses by March 1940 run from 17 to 19 according to the treatment of accidents and port losses.