U-boats were to play an important part in World War Two. Winston Churchill claimed that the U-boat war was the only time that he felt that Britain might have to contemplate surrender. Submarines had made their mark in World War One – now, just twenty years later, the impact of the U-boats was devastating.


Germany’s U-boat fleet operated out of their north German bases before the fall of France. After June 1940, they primarily used bases on the west coast of France to get to the Atlantic. U-boats operated as far a field as the east coast of South America, the west and southern coasts of Africa, north of Iceland and throughout the mid-Atlantic.

In World War One the use of submarines against unarmed merchant ships had occurred. From 1939 on the German Navy realised that merchant fleets sailing from America to Britain were highly vulnerable to attack. The Royal Navy had yet to provide full protective cover and no plane was capable of giving the convoys full support across the whole of the Atlantic. The Germans concluded that at some point across the Atlantic, the merchant ships would be at their most vulnerable with no aerial cover and little naval support. That point, they decided, would be about mid-Atlantic.

The Royal Navy found itself stretched at the start of the war. It had assumed that Italy would join Germany in the war. Therefore, the Royal Navy found that it had major commitments in various theatres of war:

With such a commitment, naval commanders had to carefully balance their resources, especially as the navy was at the forefront of the blockade against Germany as well. The Home Fleet provided a strong force around the coast of Britain. The Royal Navy was assisted by the French Navy that would hold the western part of the Mediterranean. The Royal Navy would hold the eastern part of the same sea.

When the war started in September 1939, Germany had 56 U-boats, with 46 of them operational. The Treaty of Versailles had forbidden Germany to have any submarines; therefore, in theory, she should have had no submarine crews. Germany got around this by training her crews abroad. At home, Versailles was got around by Germany training her crews in anti-submarine warfare – which was not banned. To know about anti-submarine warfare, crews had to know how submarines worked. Hence by September 1939, Germany had many well-trained submarine crews waiting to put to sea.

Initially, U-boats commanders were told to operate against merchant ships in the Atlantic in an attempt to strangle Britain’s trade. Battle instructions to submarine commanders issued in May 1939 contained the phrase:

“Fighting methods will never fail to be employed merely because some international regulations are opposed to them.”

This would later develop into unrestricted submarine warfare.

Between August 19th and August 29th, seventeen ocean-going U-boats made their way to the Atlantic. Thirteen smaller U-boats left their base to lay mines in British waters and to patrol the North Sea.

Within hours of the war being declared, U-30 attacked the liner “Athenia” and sunk it with the loss of 112 lives. The captain of U-30 exceeded his orders but the Royal Navy took this as an example that unrestricted submarine warfare had already started. It decided that merchant fleets should adopt a full convoy system as soon as it could be introduced. However, the Navy did not have the ships that could give merchant ships full support during an Atlantic crossing. To start with, a 300-mile limit to the west of Britain was introduced for British naval ships – leaving a gap of some 1,700 miles. After this, merchant ships were expected to cross independently. Those merchant ships coming from America were escorted by armed merchant cruisers and then picked up by destroyers at the 300-mile limit and escorted to port. It was not until mid-1941 that the Royal Navy could provide an escort across the whole of the Atlantic.

However, to start with, shipping losses against the U-boats were encouraging. To the end of 1939, U-boats had sunk 114 merchant ships (421,000 tons) but nine U-boats had been sunk. The Navy was reasonably encouraged as nine U-boats represented about 20% of Germany’s operational U-boat fleet. However, Germany was engaged in a very aggressive submarine building programme, and it was only a matter of time before her losses were recovered – though not the experienced crews lost at sea.

The potential of the U-boats had been seen as early as September 14th, 1939, when U39 narrowly missed sinking the aircraft carrier “Ark Royal”. U-39 was sunk and the crew was captured – but all concerned realised that it had been a close call. Just three days later on September 17th, the aircraft carrier “Courageous” was sunk by U-29 with the loss of 519 men. The Admiralty decided that aircraft carriers were too vulnerable to submarine attack and withdrew them from the submarine-hunting groups they had developed. On October 14th, the battleship “Royal Oak” was sunk by U-47 while in Scapa Flow. The aura created by such an attack was that no ship was safe, and if a mighty battleship was such a victim, merchant ships would be far easier for the U-boats.

In 1940, the U-boats started to take a real toll against merchant shipping. From January to March 1940, fewer boats were sunk than from September to December 1939. But from March on, the figures for merchant ships lost went massively up. The potency of the U-boats in the early stages of this campaign can be seen in the following figures:

Shipping sunk by Tons lost in 1940
U-boats 2,606,000
Mines 772,000
Bombers 583,000
Surface raiders 514,000
E-boats 48,000

If all the others were added together, they would be credited with sinking 1,917,000 tons of shipping – nearly 700,000 tons fewer than the U-boats alone. It was only in the winter months of 1940 that the merchant boats could find some salvation as winter storms made it far more difficult for U-boats to operate effectively.

Clearly such losses could not be sustained and an intelligence campaign started within the Admiralty to predict where U-boats would be so that convoys could be forewarned.