The U-boat, short for Unterseeboot (undersea boat), was the name for submarines used by the German Navy during the First World War (1914-18) and Second World War (1939-45). In the two Battles of the Atlantic, U-boats sank thousands of ships, but defensive strategies such as dropping depth charges, providing air cover, and, above all, the convoy system, ensured Britain was supplied with the resources it needed to continue both wars until victory was achieved on land.
U-Boats in WWI
When WWI began in 1914, the German Imperial Navy had only 20 operational submarines or Unterseeboots (undersea boats), as they were known, a name soon shortened to U-boat. Together, Britain and France had around 200 submarines. German production went into overdrive to catch up. The German navy constructed several classes of submarines to meet different requirements, such as coastal patrols, laying mines, and long-distance vessels. By 1917, Germany had 140 U-boats. While the British Admiralty focused on smaller submarines for the defence of ports, Germany opted for a vessel that could attack enemy shipping anywhere at sea. U-boats became particularly important following the Battle of Jutland in May 1916 (a strategic victory for the Royal Navy, but one with high losses), after which the giant German battleships were largely confined to port. U-boats, on the other hand, were free to roam hidden beneath the waves and attack at will any enemy target they came across in the North Sea, Atlantic Ocean, and the coastal waters of the British Isles.
The earliest U-boats, the UB class, were limited to coastal operations, but developments improved their operational capacity as the war wore on. The typical WWI U-boat had a range capable of reaching the Western Atlantic Ocean, a top speed of 17 knots, and displaced around 700 tons. U-boats carried six torpedoes. Two torpedoes could be fired from the bow and two from the stern. The submarine also had a gun which could be fired when on the surface; this had a minimum calibre of 4.1 inches (10.4 mm). A diesel engine was used when on the surface, and twin electric engines when submerged. The crew on board numbered up to 39 persons. Conditions on board were extremely cramped and uncomfortable, and made worse by the constant stench of diesel fuel, which even permeated the taste of the submariner's food.
The German Navy built a larger class of U-boats, which was unarmed but capable of carrying cargo. The Deutschland was the first of this type, put in service in 1916. Some of these cargo submarines were subsequently converted into armed vessels known as U-cruisers, although the first were not operational until 1918. The U-cruisers had an impressive range of 12,000 nautical miles, and they could well have turned the tide of the war if they had been produced earlier and in larger numbers.
The UC-class submarines were used as minelayers from 1915. With a slow speed of six knots and a limited range of 750 nautical miles, these vessels were designed to stay near coastlines and lay mines, 12 per trip. The mines were released from near-vertical tubes that had been flooded. An upgrade to the class in 1916 increased the range tenfold and the mine load to 18. The UC II class was also armed with a 3.4-inch (8.8 cm) gun. The UE-class submarine was a larger, ocean-going version of the UC-class. The UE-boats, in service from 1915, could voyage 8,000 nautical miles and carry 34 mines. A class upgrade in 1918 meant the newer UE-boats could carry 42 mines in their tubes and another 30 in deck containers.
Attack & Defence
U-boats proved very effective. The U-boat's main weapon was the self-propelled torpedo, which was fired from a torpedo tube within the submarine. Once fired, a torpedo shot towards the target, keeping just below the surface and detonating on impact. The most successful U-boat of all was the U-35, which sank 224 ships during WWI, a total of 535,000 tons of enemy shipping.
There were several countermeasures taken against submarines. The first was not to sail in a straight line or take swift evasive action if a U-boat was sighted. Hydrophone equipment could better detect the presence of submarines by registering engine noise. Contact mines were laid, which were moored to the seabed and which detonated when hit by a submarine. Magnetic mines exploded when a submarine passed near it. Enemy harbours sometimes had mines which could be detonated remotely.
Another weapon used against U-boats was the depth charge. Deployed from 1916, depth charges were canisters filled with explosives that were dropped into the sea and then detonated at a predetermined depth (thanks to the effect of water pressure on a hydrostatic valve).
A craftier defence against submarine attacks was Q-ships. Used by the Royal Navy, Q-ships were merchant ships which carried concealed guns and even torpedoes. The U-boat captain could be lulled into surfacing and trying to sink what appeared to be an unarmed vessel using his gun rather than a precious torpedo. The ruse worked on eleven occasions when the attacking U-boat was sunk, but the policy also had unfortunate consequences (see below).
Finally, the best defence of all against submarine attacks turned out to be the convoy system, adopted by the Royal Navy from May 1917, and later on by the United States. The idea was to sail many merchant vessels together and have the group protected by a number of warships. Of 88,000 ships that crossed the Atlantic as part of a convoy during the war, only 436 were hit by a torpedo.
Unrestricted Submarine Warfare
At first, there were no restrictions on how and where submarines attacked enemy ships. Unrestricted submarine warfare was fully supported by Grand Admiral Alfred von Tirpitz (1849-1930), Secretary of State of the Ministry of Marine from 1897 to 1916. As the Royal Navy attempted to blockade supplies reaching German ports, so the German Navy tried to blockade Britain from February 1915. Germany declared that any approach to Britain was to be henceforth considered a war zone and any ship German submarines came across therein – naval, merchant, or civilian – was at risk of attack. Further, no prior warning of any attack would be given. This policy was deemed a justifiable response to Q-ships. Then there occurred the shocking sinking of the RMS Lusitania.
The Cunard passenger liner Lusitania, on its way from New York to Liverpool, was sunk by a torpedo fired from U-20 on 7 May 1915 just off the southern coast of Ireland. Nearly 1,200 passengers, including 128 from the United States, lost their lives as the liner sank in under 20 minutes. The German government claimed the liner was carrying arms and ammunition for the war effort. The ship was carrying shrapnel shell cases and 4 million rounds of rifle cartridges, but these were permitted for civilian ships to carry. The Allies were shocked at the sinking and ramped up propaganda, using the incident in a recruitment drive for their armed forces.
As a result of the Lusitania furore, Germany declared the end of unrestricted submarine warfare on 1 September 1915. U-boat captains had to first surface and warn a non-naval vessel if it was about to attack. However, when the battles on land seemed unlikely to award Germany a victory, unrestricted submarine warfare was again implemented from February 1917. The strategy showed signs of working as the rate of Allied shipping losses rose from 259 ships in February to 423 in April. These losses could not be replaced fast enough by shipyards. The convoy system, though, began to reap rewards, and Allied losses were reduced to around half of what they had been by the end of 1917. By 1918, the rate of construction of new Allied ships was outstripping losses. The German Navy, meanwhile, was losing U-boats at an alarming rate as defence techniques improved.
In WWI, U-boats sank over 5,000 ships, sending more than 12 million tons of enemy shipping to the bottom of the sea (Blair, 18). Impressive though these figures are, in the end, they were not sufficient to win what became known as the (First) Battle of the Atlantic. Britain's sea supply lines did not collapse. 178 U-boats were sunk during the conflict. 5,000 German submariners were either killed, wounded, or captured. Germany lost WWI as the armistice was signed on 11 November 1918. All remaining German U-boats were then handed over to the victors.
U-Boats in WWII
When WWII began, submarine design had not changed radically since 1918. Germany had been forbidden from possessing submarines under the terms of the Treaty of Versailles, which had formally concluded WWI. Now, once again, Britain tried to blockade Germany, and German submarines were used to try and sink as many ships supplying Britain with food, raw materials, and weapons from the Americas as possible. It was a second Battle of the Atlantic, although U-boats also operated in other theatres, notably in the Mediterranean and the North Sea.
U-boats were used in some daring raids on ports, notably when U-46, captained by Günther Prien (1908-1941), sank the battleship HMS Royal Oak at Scapa Flow in Scotland in October 1939. With the Fall of France in the summer of 1940, the German Navy could establish U-boat bases much closer to the Atlantic Ocean. There were also U-boat bases on the coast of West Africa and in the Mediterranean. The primary focus of the U-boat campaign, though, was to try and reduce supplies reaching Britain, forcing that country to surrender.
The lessons from WWI on the value of convoys were initially ignored by the Allies, and a system of submarine-hunting groups based around an aircraft carrier was employed instead. When the latter strategy proved a failure (notably with the sinking of the aircraft carrier HMS Courageous by U-29), the convoy system was adopted by the British, with immediate and lasting success, especially when air cover was added. However, when the United States entered the war in 1942, the US Navy, inexplicably, did not adopt a convoy system until such losses were borne that it could no longer not use the system. As the British prime minister Winston Churchill (1874-1965) noted, "The only thing that ever really frightened me during the war was the U-boat peril" (Boatner, 135).
Specifications
WWII U-boats were faster than their WWI counterparts and could carry more torpedoes, typically 12 per trip. The standard type was the 7C, which could dive to a depth of 985 ft (300 m), fire from forward or stern tubes, and had a range of 12,600 nautical miles (23,000 km). A 7C measured around 220 feet (67 m) in length, and later versions had a top surface speed of 17 knots (or 7.6 when submerged). These U-boats were also armed with at least one 3.4-inch (88 mm) and one 0.78-inch (20 mm) gun.
Submariners were volunteers and considered themselves elite specialists. Conditions inside a U-boat were extremely cramped, some crew having only collapsible beds or hammocks. There were two tiny toilet cabins for the crew of around 45 men. Food available was dried meat, tinned goods, cheese, and hard bread. Heating and ventilation systems were rarely adequate, and everything was always damp.
The 9D U-boat was slightly bigger than the 7C and, with a range of up to 32,000 nautical miles, was used as a cruiser or to lay mines. Larger U-boats were used to provide smaller ones with fuel, torpedoes, and provisions. Midget submarines were used to attack port installations.
As in WWI, submarine warfare was at first restricted, and merchant ships were meant to be warned before a torpedo was fired. As merchant ships began to be better armed, so unrestricted warfare became the norm. The favoured attack mode was to do so on the surface and at night.
Eyewitness Accounts
German submarine captains had an advantage in the first years of the war in that they could decode Allied messages using a German Enigma machine. One U-boat officer, Lieutenant Ernst von Witzendorff, recalls:
I must say in this time we were young naval officers and we were interested to do our duty and to be successful. When we attacked in daytime looking through our periscope, or attacking in the night being on the surface, we saw these big merchant ships like animals creeping over the sea [and] then we were eager to sink them and we didn't think on those poor merchant seamen which were on the merchant ships.
(Holmes, 168)
One merchant seaman, Vernon Miner, recalls what it was like to be attacked by a U-boat:
I was steering the ship when the lookout reported that there was a U-boat on the starboard beam. The Chief Officer who was in charge of the watch ordered me to alter course to bring the U-boat astern of us. My feeling was one of excitement. This is it, I'm going to come home covered with glory – decorated – I'll strangle these submarines with my bare hands. Then the firing started and the first shell that hit the ship, the ship shuddered...There's a feeling that God is on your side but he certainly wasn't, and this is the period when it's frightening, the moment of truth. The order to abandon ship eventually comes and you look down on that grey North Atlantic, which doesn't look all that bad from the deck of a ship about twenty feet above the water but down at lifeboat level it looks rather ominous...
(Holmes, 89)
The Wolf Packs
Admiral Karl Dönitz (1891-1980), who was head of the German U-boat service (and from 1943 the entire German navy), had himself commanded a submarine in WWI. Dönitz developed the idea of deploying U-boats in large groups of 8 to 20 submarines (or more rarely up to 50), which became known as wolf packs. A pack could spread itself out in a line up to nautical 100 miles (185 km) long and so detect the presence of an oncoming convoy. The pack could then reconverge and attack in such numbers as to wipe out a convoy's protecting ships, allowing the U-boat captains to pick off the choicest merchant vessels at leisure, often over two nights. U-boat captains did not usually stop to pick up survivors – there was little space for them in a U-boat anyway – and this was particularly so after the sinking of the Laconia in September 1942, when a miscommunication resulted in a US airplane attacking the U-boat that was responsible for the sinking but was then rescuing survivors.
Submarine countermeasures improved as the war went on, eventually giving surface ships the advantage. Sonar (ASDIC) could hear the engines of a U-boat. Radar could detect a periscope. Another device used by the US Navy permitted captains to locate a U-boat when it used its wireless radio. High-frequency direction-finding equipment was in use from 1941 by ships and aircraft. The Fido was a target-seeking torpedo, which could be dropped into the sea and relied upon to find a submerged U-boat.
U-boats also faced mines, which came in several deadly varieties: contact, magnetic, acoustic, and pressure mines. A mine could contain around 775 lb (350 kg) of explosives. Depth charges, containing up to 300 lb (136 kg) of explosive and effective up to a depth of 985 ft (300 m), could be deployed in wide arced patterns to maximise the chances of damaging a nearby submarine. Depth charges were very effective: "Of all German U-boats destroyed 43% were sunk with D/Cs" (Dear, 33). Apart from diving deep or moving erratically, a submarine captain could release bubbles as a decoy against detection.
Reckoning
Just as there were air aces with extraordinary success rates, so, too, there were U-boat captains who notched up a formidable list of victims. Lieutenant Otto Kretschmer (1912-1998) sank 46 ships, worth 273,000 tons.
Dönitz believed that U-boats could force Britain to surrender, but he was never given the number of submarines he required, given the strains on Germany's war production. There were technological developments such as the Schnorchel (snorkel), which permitted submarines to take in oxygen and pump out fumes while still below the surface, but these came too late in the war to have any significant effect on the outcome.
Nevertheless, U-boats took a terrible toll on Allied shipping. In 1940, 1,345 ships were sunk for the loss of 24 U-boats; in 1941, 1,419 ships versus 35 U-boats sunk; in 1942, 1,859 ships versus 86 submarines sunk; in 1943, 812 ships versus 242 U-boats lost. The Allies had perfected the convoy system with coordinated air defence and had better radar. In the end, then, the U-boat service had failed. In total, 3,500 Allied ships, 14.5 million tons of shipping, were sunk in WWII's Battle of the Atlantic, but 765 U-boats had been sunk (around 65% of those built). The toll for the German Navy was too high a price to pay. In addition, the loss rate of U-boat seamen was around 75% (28,000 men), the highest rate in all the armed services. U-boats had been iron coffins for far too many young men.
