U-boats

U-boat is the anglicized version of the German word U-Boot (help·info), itself an abbreviation of Unterseeboot (undersea boat), and refers to military submarines operated by Germany in World War I and World War II. Although in theory U-boats could have been useful fleet weapons against enemy naval warships, in practice they were most effectively used in an economic-warfare role, enforcing a naval blockade against enemy shipping. The primary targets of the U-boat campaigns in both wars were the merchant convoys bringing supplies from Canada and the United States to Europe. Austrian submarines of World War I were also known as "U-boats".

The distinction between U-boat and submarine is common in English-language usage (where U-boat refers exclusively to the German vessels of the World Wars) but is unknown in German, in which the term U-Boot refers to any submarine.

At the start of World War I, Germany had twenty-nine U-boats; in the first ten weeks, five British cruisers had been lost to them. In September, U-9 sank the obsolete British warships Aboukir, Cressy and Hogue (the "Live Bait Squadron") in a matter of minutes[citation needed].

For the first few months of the war, U-boat anti-commerce actions observed the current "prize rules" which governed the treatment of enemy civilian ships and their occupants. Surface commerce raiders were proving to be ineffective, and on 4 February 1915, the Kaiser assented to the declaration of a war zone in the waters around the British Isles. This was cited as a retaliation for British minefields and shipping blockades. Under the instructions given to U-boat captains, they could sink merchant ships, potentially neutral ones, without warning. A statement by the U.S. Government, holding Germany "strictly accountable" for any loss of American lives, made no material difference.

On 7 May 1915, U-20 sank the liner RMS Lusitania with a single torpedo hit. The sinking claimed 1,198 lives, 128 of them American civilians, including noted theatrical producer Charles Frohman and Alfred Vanderbilt, a member of the prestigious Vanderbilt family. The sinking deeply shocked the Allies and their sympathizers because an unarmed civilian merchant vessel was attacked without any warning. According to the ship's manifest, Lusitania was carrying military cargo.

The initial U.S. response was to threaten to sever diplomatic relations, which persuaded the Germans to re-impose restrictions on U-boat activity. The U.S. reiterated its objections to German submarine warfare whenever U.S. civilians died as a result of German attacks, which prompted the Germans to fully re-apply prize rules. This, however, removed the effectiveness of the U-boat fleet, and the Germans consequently sought a decisive surface action, a strategy which culminated in the Battle of Jutland.

Although the Germans claimed victory at Jutland, the British Grand Fleet remained in control at sea. It was necessary to return to effective anti-commerce warfare by U-boats. Vice-Admiral Reinhard Scheer, Commander in Chief of the High Seas Fleet, pressed for all-out U-boat war, convinced that a high rate of shipping losses would force Britain to seek an early peace before the United States could react effectively.

The renewed German campaign was effective, sinking 1.4 million tons of shipping between October 1916 and January 1917. Despite this, the political situation demanded even greater pressure, and on 31 January 1917, Germany announced that its U-boats would engage in unrestricted submarine warfare beginning 1 February. On 17 March, German submarines sank three American merchant vessels, and the U.S. declared war in April 1917.

In the end, the German strategy failed to destroy Allied shipping before U.S. manpower and materiel could be brought to bear in France. An armistice became effective on 11 November 1918.

At the end of World War I, as part of the Paris Peace Conference, 1919, the Treaty of Versailles restricted the total tonnage of the German fleet. The treaty also restricted the independent tonnage of ships and forbade the construction of submarines. Before the start of World War II, Germany started rebuilding U-boats and training crews, hiding these activities as "research" or other covers, so that when World War II started, Germany already had a few U-Boats ready for war.

During World War II, U-boat warfare was the major component of the Battle of the Atlantic, which lasted the duration of the war. Germany had the largest submarine fleet in World War II, since the Treaty of Versailles had limited the surface navy of Germany to six battleships (of less than 10,000 tonnes each), six cruisers and 12 destroyers. Prime Minister Winston Churchill wrote "The only thing that really frightened me during the war was the U-Boat peril".

U-boat Pens in St Nazaire, FranceIn the early stages of the war, the U-boats were extremely effective in destroying Allied shipping, ranging from the Atlantic coast of the United States and Canada to the Gulf of Mexico, and from the Arctic to the west and southern African coasts and even as far east as Penang. It is even rumored that one German U-boat managed to make it all the way down to Galveston Bay, Texas. Because speed and range were severely limited underwater while running on battery power, U-boats were required to spend most of their time surfaced running on diesel engines, diving only when attacked or for rare daytime torpedo strikes. The most common U-boat attack during the early years of the war was conducted on the surface and at night. This period, before the Allied forces developed truly effective antisubmarine warfare (ASW) tactics, was referred to by German submariners as the "happy time."

U-boat 534, Birkenhead Docks, Merseyside, England. The U-boat was essentially a sophisticated launch platform for its main weapon, the torpedo. German World War II torpedoes were straight runners, unlike the homers and pattern-runners of later in the war. They were fitted with one of two types of exploder, one which detonated the warhead upon impact with a solid object, another which detonated magnetically upon sensing a large metal object nearby. Ideally, when using magnetic exploders, the commander would set the torpedo's depth so it passed just beneath the keel. The explosion would create a gas bubble, and the ship would break in two. In this way, even large or heavily-armored ships could be sunk or disabled with a single well-placed hit. In practice, however, both the depth-keeping equipment and magnetic exploders were notoriously unreliable early in the war. Torpedoes would often run at an improper depth, detonate prematurely, or even fail to explode. This was most evident in Operation Weserübung, the invasion of Norway, where various skilled Captains failed to inflict damage on British transports and warships because of faulty torpedoes. The magnetic exploder was eventually phased out, and the depth-keeping problem was solved in early 1942.

Later in the war, Germany developed an acoustic homing torpedo. These were primarily designed to combat escorts. The acoustic torpedo was designed to run straight to an arming distance of 400 meters and then zero in on the loudest noise detected. This sometimes turned out to be the U-boat itself, and at least two submarines may have been sunk by their own homing torpedoes (problems with steering mechanisms on normal torpedoes made them occasionally lethal to the firing boat as well). Additionally, it was found these torpedoes were only effective against ships moving at greater than 15 knots. U-boats also adopted "pattern-running" torpedoes which ran to a preset distance, then traveled in either a circular or ladder-like pattern. When fired at a convoy, this increased the probability of a hit in case the weapon missed its primary target.

ACCESSORIES