U-32, a Type VIIA submarine. Image copyright Imperial War Museum, reference IWM HU1011
At the outbreak of war Germany had only 57 U-boats. Less than half of these had the required range to operate in the Atlantic. This force was rapidly expanded under Karl Donitz, Officer Commanding U-boats.
Until 1945 all the U-boats were based on First World War designs. More than half (704) were of Type VII or its variants. Together with the larger Type IX these 'Atlantic boats' spearheaded Germany's war at sea.
The diesel-electric Type VII:
- was designed as a submersible, ocean-going torpedo boat
- in its original form it was only 218 feet (64.5 metres) long
- was very manoeuvrable and hard to locate
- had a surface speed of 16 or 17 knots
- could submerge in 30 seconds
- had an average range of over 4,000 miles.
Until June 1940 U-boat operations in the Atlantic were limited by several factors:
- no more than ten boats were available at any one time
- many torpedoes were faulty
- Operations around Norway kept numbers down
- German High Command placed strict limits on U-boat activities, fearing
- American entry into the war.
Even so, by June over 200 merchant ships had been sunk. British warships had also suffered significant losses.
After the Fall of France in June 1940 the Germans used the French Atlantic ports as bases. This meant the U-boats could reach far out into the Atlantic and Mediterranean.
Despite the shortage of submarines and air support, the U-boats became increasingly successful. They also began to use small 'pack attacks' against the largely undefended British convoys. The introduction of the 'wolf pack' system in 1940 resulted in heavy British losses. Several U-boats would attack a convoy at night on the surface. They would withdraw by day but attack again the following night.
By late October 1940, the British Admiralty feared the Battle of the Atlantic was already lost.