The German threat

In 1939 the German Navy (Kriegsmarine) was not strong enough to risk a major fleet battle with the Royal Navy, which was still the largest navy in the world.  Instead, it made Britain’s sea trade its prime target.  The German aim was to defeat Britain by ruthlessly attacking her maritime supply lines, especially in the North Atlantic.

In this long and bitter campaign the Germans were to use submarines (U-boats), mines, surface warships, armed merchant ships and aircraft.  As in the First World War, however, the U-boats were to pose the deadliest threat to Britain’s survival.

"...the only thing that ever really frightened me during the war was the U-boat peril." Winston Churchill (The Second World War)

The sinking of the 'Athenia'

The Battle of the Atlantic began with the sinking of the Liverpool-based passenger liner 'Athenia' (Donaldson Atlantic Line) by German submarine U-30 on the first day of the war.  'Athenia' had sailed from Liverpool for Montreal at 4pm on 2 September 1939.  She was torpedoed by the German submarine U-30, without warning, at 7.30pm the following day, about 250 miles north-west of Ireland.  Of her 1,103 passengers and 315 crew, 93 passengers (including 22 Americans) and 19 crew members were lost.  Britain had declared war on Germany just eight hours earlier.

The Captain of U-30 was Commander Kapitanleutnant Fritiz-Julius Lemp.  The 26 year old Lemp had wrongly assumed from the 'Athenia's lone, zig-zag course that she was an armed auxiliary cruiser.  He had, without warning, sunk an unarmed passenger ship, contrary both to international law and to the strict instructions of U-boat Command.  He had also broken a pre-war international agreement by offering no help to survivors. 

The horrific fate of the ‘Athenia’ was widely linked with that of the ‘Lusitania’ during the First World War.  It was hoped that this would help fuel anti-German feeling in the United States, as had happened following the ‘Lusitania’ disaster in 1915.

The mine offensive, 1939-41

In the early months of the war German U-boats, destroyers, minelayers and aircraft laid thousands of mines in strategic areas all around the British coast.  By December 1941 almost 400 British Allied and neutral merchant ships had been sunk, and many more damaged, by German mines in British waters.

The huge, undeclared minefields off the British coast also gave the German High Command the cover it needed to begin unrestricted U-boat warfare.  Sudden sinking in British waters could now be blamed on mines, and losses increased dramatically.

The oil tanker ‘El Oso’ (7,267 tons) was the first of many ships struck by German mines in or near the port of Liverpool during the war.  She was sunk by a mine laid by a U-boat in early January 1940.  Most other mines which struck ships near the port of Liverpool were dropped by aircraft between early 1940 and January 1942.

Surface warships

At the start of the war the German Navy had far fewer surface warships than the Royal Navy.  Those which they had, however, were modern, fast, powerful, and designed for worldwide attacks on enemy trade.  In the early war years these German warships enjoyed some notable successes in the Atlantic and elsewhere, causing great anxiety to Britain and her allies.  The sinking of the battleship ‘Bismarck’ in May 1941, however, largely ended the threat of German surface warships in the Atlantic.

"Even a single raider loose in (the) North Atlantic requires employment of half a battle fleet to give sure protection."
Winston Churchill, First Lord of the Admiralty, December 1939.

The 42,900 ton ‘Tirpitz’ and her sister ship ‘Bismarck’ were the largest and most powerful German warships to serve in the Second World War.  ‘Tirpitz’ was not completed in time to join ‘Bismarck’ on her ill-fated North Atlantic voyage of May 1941.  Instead, in January 1942 she sailed from Wilhelmshaven for Norwegian waters, where she was to remain for the rest of the war.   Until late 1943 she posed a major threat to Allied convoys carrying war supplies via the Arctic route to northern Russia.   In particular, the threat of her presence in July 1942 caused the scattering and subsequent loss of the greater part of Convoy PQ 17.  In the later war years she was damaged by British midget submarines and aircraft, and finally capsized due to an attack by the Royal Air Force.


By late 1940 German aircraft based in France were posing a threat to Allied shipping in the Atlantic.  In particular, a squadron of long-range, Focke-Wulf ‘Kondor’ or ‘Kurier’ aircraft had been established near Bordeaux.  Flying up to 600 miles into the Atlantic, the ‘Kondors’ could direct U-boats onto convoys and bomb the almost defenceless merchant ships.  In their first two months of operations they sank 30 merchant ships, totalling 110,000 tons.

Fortunately for Britain, the Kriegsmarine was never able fully to control Luftwaffe missions over the Atlantic.  Nor was it allowed by Hitler to establish its own air-arm, and so launch combined operations by sea and air.  As a result, German air power was largely directed elsewhere.

The U-boat

In the late 1930s Karl Donitz, Flag Officer in command of U-boats, had estimated that Germany would need at least 300 U-boats in the event of war with Britain.  In September 1939, however, Germany had only 57 U-boats, of which less than half had the range to operate in the Atlantic.

"The submarine arm is still much too weak to have decisive effect on the war." Grand Admiral Raeder, Commander-in-Chief of the German Navy, 3 September 1939.

Between 1939 and early 1945 all German U-boats on active service were based on the First World War designs.  More than half (704) were of Type VII or its variants, the largest class of warships ever built.  Together with the larger Type IX, the Type VII ‘Atlantic boats’ bore the brunt of Germany’s war at sea.

The Type VII U-boat was a diesel electric vessel, designed as a submersible, ocean-going torpedo boat.  In its original form it was only 64.5 metres long and of 745 tons displacement.   This small size made it very manoeuvrable and difficult to locate, especially when on the surface at night.  It had a fast surface speed of 16 or 17 knots, and could submerge in just 30 seconds.  Its average range was over 4,000 miles which made it well suited to ocean-going operations.  Until mid-1943 it was to enjoy remarkable success in the Atlantic campaign.

Early U-boat successes

In the early hours of 14 October 1939 the old British battleship ‘Royal Oak’ was sunk at her moorings at the naval base at Scapa Flow (Orkney Islands, off north–east Scotland) by torpedoes fired by German submarine U-47.  Nearly 800 officers and crew were lost.

Until June 1940, U-boat operations in the Atlantic were limited because no more than 10 boats were usually available at any one time.   Faulty torpedoes and the withdrawal of some boats to support operations in Norway were further handicaps.  German High Command, fearing American entry into the war, especially after the ‘Athenia’ incident, also placed strict limits on U-boat activities.  Even so, by June 1940 U-boats had sunk over 200 British, Allied and neutral merchant ships in the Atlantic at a rate of 22 per month.  Several important successes had also been achieved against British warships.

The U-boats' 'Happy Time'

After the Fall of France in June 1940 the Germans were able to use the French Atlantic ports as bases.  U-boats could now reach out into the western part of the North and Central Atlantic, and into the Mediterranean.  Germany soon declared virtually unrestricted U-boat warfare around the coast of Britain and out into the Atlantic.

Despite a continuing shortage of boats and of air support, Donitz’s ‘U-boat Arm’ became increasingly successful.   For the first time small U-boat ‘pack attacks’ were used, with devastating effect, against the still largely unprotected British convoys.  By late October 1940 the Admiralty feared that the U-boats were on the brink of victory in the Atlantic.  By March 1941, however, the peak successes of the U-boats’ ‘Happy Time’ had passed.  In June the German attack on Russia gave Britain vital relief both from the threat of invasion and from the U-boat siege.

Much of the success of the U-boats’ ‘Happy Time’ in the North Atlantic was due to the skills and experience of several of Donitz’s ‘ace’ commanders, such as Gunther Prien, Otto Kretschmer and Joachim Schepke.  These men became national heroes in Germany.  Almost a third of all Allied merchant ships sunk by U-boats in the Atlantic during the war (i.e. about 800) were the victims of about 30 experienced officers who had joined the German Navy by 1935.

Otto Kretschmer, one of Germany’s most successful U-boat ‘aces’, was commander of U-99 which sank 40 British and Allied merchant ships (about 250,000 tons) in under nine months’ active service from July 1940.  Kretschmer, nicknamed ‘The Golden Horseshoe’ by his men, had two golden horseshoes mounted on the conning tower of U-99 to bring him luck.  U-99’s luck finally ran out on 17th March 1941, when she was sunk in a convoy battle south-west of Faroe Islands by the destroyer 'HMS Walker'. Kretschmer and most of his crew, however, survived to become prisoners of war.

The sinking of the 11,000 ton passenger liner ‘City of Benares' (Ellerman City Line) brought home the ruthlessness of the U-boats' 'Happy Time' to newspaper readers and radio listeners all over the world.

The children’s ship

On 17 September 1940 the ‘City of Benares’ was sailing as commodore ship (leading vessel) on the19-ship slow convey OB2123.  On board were 100 children, 90 of whom were on a government scheme to evacuate them from heavily-bombed British cities to the safety of North America.  At 10pm that night, in bad weather some 600 miles out in the Atlantic, she was torpedoed, without warning, by the German submarine U-48.  The convoy’s screen of naval escort ships had left for other duties some hours earlier.  The ‘City of Benares’ sank in forty minutes. Of the 406 people on board 250 were lost, including 81 children.

Life on a U-boat

"The heat. The stench of oil. Lead in my skull from the engine fumes.  I feel like Jonah inside some huge shellfish... sheathed in armour"
German war photographer on board U-96 in 1941.

The lives of the 40,000 men who served in the German U-boat fleet bore little relation to the glamorous image which their activities inspire in the German public mind.  The U-boats were cramped, smelly, unhygienic and almost unbearably claustrophobic.  In a typical U-boat the bow compartment (at the front), measuring just twelve feet (3.6 metres) across, housed some 25 men, several 22ft (6.7 metres) torpedoes, loading carriages and other equipment.  Each bunk was used by two or more men, on a shift system.

The wolf pack

Towards the end of 1940 Admiral Donitz introduced the ‘wolf pack’ system of using several U-boats to attack a convoy at night on the surface.  This required convoys to be located and shadowed by aircraft or U-boats.   The U-boat pack would then gather for a surface attack at night, withdrawing by day but attacking again the next night.  Later in the war wide patrol lines of U-boats were positioned across the main Atlantic convoy to trap the convoys.  Not until mid 1943 were the Allies able finally to defeat the ‘wolf pack’ tactics used by the U-boats in the North Atlantic

The secret threat

Until late 1943 the German Navy, via code breakers, had the invaluable asset of being able to read British and Allied radio codes for convoys.  They were therefore often able accurately to predict the numbers, types and locations of Allied convoys.

It was not until mid-1941, however, that British code breakers began to crack the complex Enigma codes used by the German Navy.