The Happy Time and the Wolfpacks

Before the fall of France, an ocean-going U-boat had to spend a substantial part of every patrol passing through the North Sea and around the British Isles before it reached the Atlantic routes. The occupation of the French coast removed much of that transit. The first U-boat visited Lorient on 22 July 1940, and the ports at Lorient, Brest and Saint-Nazaire became forward bases from which boats could spend more of each patrol in the approaches used by convoys from North America.

The geography favoured interception rather than blockade by a continuous line. Homeward HX and slower SC convoys approached Britain through the North Atlantic and, from July 1940, generally entered by the North Channel. Dönitz could spread boats across likely convoy routes, use the first contact report to draw others toward the convoy, and then attack after dark. Long-range Focke-Wulf Fw 200 aircraft operating from occupied France added another search instrument, although air and submarine cooperation remained less systematic than German plans implied.

The British problem was equally geographic. Ocean escorts could not yet remain with every convoy from North America to Britain, escort groups were often assembled from whatever destroyers, sloops, corvettes and trawlers were available, and the handover between ocean and Western Approaches escort could leave a convoy exposed. The autumn battles happened where the convoy routes converged toward Britain and where several U-boats could be concentrated faster than local escorts could reinforce.

The group tactic depended on communications. Boats patrolled separately across broad search lines. A submarine that found a convoy was expected to maintain contact and report its position rather than spend its first opportunity in an isolated attack. BdU could then order nearby boats to converge. The 'wolfpack' was therefore not a formation moving together through the Atlantic; it was a temporary concentration created around a convoy contact.

The decisive tactical feature in 1940 was the night surface attack. Contemporary ASDIC was designed primarily to search for a submerged submarine ahead of an escort. A Type VII on the surface presented a low silhouette, could make much greater speed than when submerged and could approach from inside or between convoy columns. Once the attacker was among merchant ships, escorts had difficulty distinguishing the submarine, maintaining contact and dropping depth charges without endangering the convoy itself.

The method did not make every convoy helpless. Weather broke contact, escorts drove boats off, radio reports could be late or inaccurate, and a concentration could arrive after the convoy had escaped. What October 1940 demonstrated was that when contact was maintained and several experienced commanders reached the same convoy, the existing escort system could be overwhelmed for a night. SC 7 and HX 79 were attacked in immediate succession and lost thirty-two ships between them.

The German Type VII was the central weapon of the campaign because its surface speed, range and compact silhouette suited the new tactic. Larger Type IX boats added endurance farther into the Atlantic. Both types remained vulnerable once forced below the surface, but in the second half of 1940 the most successful attacks were often conducted before the escort could establish an underwater contact at all.

British escort strength was expanding but uneven. Flower-class corvettes were entering service in growing numbers, while old American destroyers transferred under the destroyers-for-bases agreement began arriving in September 1940 and needed refit before useful employment. Destroyers, sloops, trawlers and corvettes carried ASDIC and depth charges, but many escorts lacked radar and the trained group organisation that later allowed one ship to hold contact while others attacked or protected the convoy.

Air coverage was another incomplete layer. Coastal Command Sunderlands and other patrol aircraft could force a U-boat to submerge and could search large areas, but aircraft numbers, range and anti-submarine weapons were still inadequate for continuous ocean cover. The Fw 200 Condor, by contrast, could range far into the Atlantic from France and threaten merchant ships directly as well as report convoy positions. The technological balance in this phase was therefore not one machine defeating another; it was a mismatch between a new attack method and an escort system still organised for the submerged threat.

SC 7 lost twenty merchant ships between 16 and 19 October. HX 79 was located as the SC 7 battle ended and lost another twelve ships during the night of 19–20 October despite a substantial local escort. Those two battles became the clearest demonstration of what several surfaced U-boats could do when they reached a convoy together.

The pressure continued into winter. HX 90 lost eleven ships on 1–3 December, while other HX and SC convoys also suffered repeated attacks. These losses did not mean the convoy system had failed; ships travelling in convoy remained easier to escort and rescue than independent traffic. They did show that the escort system needed more ships, more continuous coverage, better tactical organisation and a way to detect submarines on the surface at night.

March 1941 produced a different kind of loss. U-70 was sunk during the battle around OB 293, U-47 disappeared after taking part in the same operation, and ten days later U-100 and U-99 were destroyed during the attack on HX 112. Joachim Schepke was killed and Otto Kretschmer captured. The boats were replaceable in material terms; the simultaneous removal of several of the most experienced commanders was not.

The operational framework follows S. W. Roskill's official history and the wartime-derived US Navy Operations Evaluation Group study of antisubmarine warfare, which explicitly defines July 1940 to March 1941 as the period of night surfaced convoy attacks. Individual German attacks are checked against surviving U-boat war diaries and the British interrogation reports produced after U-70, U-99 and U-100 were lost.

Convoy-loss totals are kept separate from individual U-boat claims. The latter could be inflated in combat reports and propaganda, while convoy records allow losses to be checked ship by ship. The February–March British command changes are checked against Western Approaches records, Churchill's 6 March directive and Coastal Command's official despatch.