The British response to the German U-boat menace in WW2

Like most Engelandvaarders, young Jan ter Doest traveled the last stretch

on his way to Britain by boat. On a bright January morning in 1943 he boarded a British troop ship, the Ormonde. As part of a convoy the Ormonde sailed away from Gibraltar’s rock for a perilous journey across the Atlantic Ocean towards Britain. In the year before, more than a thousand allied vessels were lost to attacks by German submarines, also known as U-boats.

1.The Ormonde as a cruise ship before she was recruited by the Royal Navy

Sailing in convoy

During the Second World War, Britain needed to secure its vital import of food, equipment and raw materials from overseas, notably from North America and the empire. To hinder these supplies Germany patrolled the Atlantic shipping lanes with U-boats, their torpedoes at the ready to sink any spotted merchant ship. In turn, the British counteracted the U-boat menace by sailing in convoy, their vessels escorted by the Royal Navy.

2. Approximate locations of merchant ships sunk by U-Boats between August 1942 and May 1943

Convoy types and their tactics

Convoys were as fast as their slowest ship. Therefore they were divided into three types: fast, medium and slow.

A fast convoy consisted of a small number of large ocean liners, mainly former cruise ships recruited by the Royal Navy. This type carried both merchandise and troops. As a unit, it could transport between twenty and thirty thousand men at a cruising speed of around thirteen knots (fifteen miles per hour). The medium and slow convoys carried only merchandise. With up to fifty vessels, often quite old and basic, a medium convoy sailed at a speed of nine knots while a slow convoy limped along at four to seven knots. Staying well away from coastal waters where German Focke Wulf bombers patrolled to pass on the convoy’s position to U-boats, hundreds of allied ships were daily herded across the Atlantic ocean.

The logistic preparation of each convoy required several weeks. A convoy was scheduled as accurately as an express train to arrive exactly on time at a fixed ‘rendez-vous’, often in the middle of the ocean. There it was met by a destroyer escorte, which guided it through the more dangerous waters, until the ships were dispersed to unload and reload at their respective ports.

3. Part of a convoy as seen from an escorting warship, June 1942

A seemingly random pattern of zigzagging was meant to fool the U-boats.

Several times per hour all vessels would alter their course like a giant flock of birds. The vessel in charge was the Commodore’s ship or flag ship, flying a pennant, in the centre of the convoy. Its task was to indicate the course and speed of the fleet, by means of hoisting flags or sending light signals. To make sure all vessels followed the same pattern, the fast and maneuverable destroyers enforced discipline. Engelandvaarder Bart Bredero was one of the passengers who witnessed the spectacle on deck. In his memoirs he wrote:

“The escorte ships, sleak as hounds, dashed among the ocean liners, snarling with their loud hailer to any vessel that did not comply fast enough with the system”.

During fog and at dusk, the zigzagging ceased, because U-boats could only aim their torpedoes visually. In darkness the convoy kept a steady course with all lights turned off. At night, it was strictly forbidden to smoke outside. Even the glowing butt of a sailor’s cigarette might convey a ship’s presence to the submarine’s vigilant eye, the periscope.

4. Sailors during a rest period in their living quarters on board a cargo vessel, January 1942

More German submarine power

Since Germany had established a U-boat station at Lorient, on the French west coast, both range and number of submarines saw a vast increase. Under cover of night a number of U-boats would encircle a convoy like a ‘wolfpack’ to attack it from multiple directions.

Although the German U-boats with their dreaded torpedo’s posed a severe threat, they also had their weaknesses. For various reasons, submarines were often forced to surface, which made them vulnerable to attacks. It was only above water that they could move fast, making use of their powerful diesel engines. Without air these engines could not operate so when submerged, U-boats were propelled by means of their much weaker electric batteries, at a slow three knots.

They also had to come up for recharging their batteries by means of their engines. At the crucial moment of firing their torpedoes, the submarines kept just below the water’s surface, only their periscope tube piercing the waves.

The allied escorte had its own drawbacks. When under threat, the destroyers defended their convoy by sending ‘depth charges’ into the deep. At best, these explosives detonated near the submarine by water pressure, subjecting the target to a powerful and destructive hydraulic shock. This action was meant to rupture a U-boat’s pressure hull. However, the blast itself could cause a curtain of debris in the sea, which disturbed the escorte’s own sonar system. If the U-boat had not been damaged and therefore had to be attacked again, the submarine often could not be located any more.

5. Detonating depth charges launched from a British destroyer, December 1942

At times hard decisions had to be made in the interest of the group. When a ship was damaged, it was left to its own devices. Sadly, the convoy had to keep moving at all cost.

Ultimately, a combination of new tactics, a large shipbuilding program and scientific ingenuity worked in favour of the allies. For example, more sophisticated types of anti submarine depth charges were developed.

In particular when radar was added to the already existing sonar systems, the Germans did not have an adequate response. Submarines could now be traced day and night, whether they were at the surface or submerged. The ‘threat from the deep’ gradually diminished and the Germans were forced into the defensive. In the relentless ‘Battle of the Atlantic’, the roles had switched for good.

Literature:

Arnold Hague Database: http://www.convoyweb.org.uk/mkf/index.html. Retrieved: 28-11-2018
Booth, O. & Walton, J. (1998). The Illustrated History of World War II. Chartwell Books Inc; Edison, New Jersey
Bredero B. Memoirs. Nationaal archief. Archiefinventaris 2.19.127. Index 103.
Gwatkin-Williams, R.S. (2009). Article first published in the Daily Telegraph on 16-09-1939. https://www.telegraph.co.uk/history/world-war-two/6188120/World-War-2-Convoy-was-the-key-to-defeat-of-U-boats-last-time.html. Retrieved 28-11-2018
MET office, digital library, weather desk & archives: https://digital.nmla.metoffice.gov.uk/digitalFile_aca66ce9-a428-4599-974b-ff238346a4b6/ Retrieved: 28-11-2018