U-boat is an
anglicised version of the German word
U-Boot [ˈuːboːt] a shortening of
Unterseeboot, literally "underseaboat." While the German term refers to any
submarine, the English one (in common with several other languages) refers specifically to
military submarines operated by Germany, particularly in the
First and
Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare role (
commerce raiding) and 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 other parts of the
British Empire, and from the United States to the United Kingdom and (during the Second World War) to the Soviet Union and the Allied territories in the Mediterranean. German submarines also destroyed Brazilian merchant ships during World War II, causing Brazil to declare war on the Axis powers in 1944.
Early U-boats (1850–1914)
The first submarine built in Germany, the three-man
Brandtaucher, sank to the bottom of
Kiel harbor on 1 February 1851 during a test dive.
[1][2] The
inventor and
engineerWilhelm Bauer had designed this vessel in 1850, and
Schweffel & Howaldt constructed it in
Kiel.
Dredging operations in 1887 rediscovered
Brandtaucher; it was later raised and put on historical display in Germany.
There followed in 1890 the boats
WW1 and
WW2, built to a
Nordenfelt design. In 1903 the
Friedrich Krupp Germaniawerft dockyard in Kiel completed the first fully functional German-built submarine,
Forelle,
[3] which
Krupp sold to Russia during the
Russo-Japanese Warin April 1904.
[4] The
SM U-1 was a completely redesigned
Karp-class submarine and only one was built. The
Imperial German Navy commissioned it on 14 December 1906.
[5] It had a double hull, a
Körtingkerosene engine, and a single torpedo tube. The 50%-larger
SM U-2(commissioned in 1908) had two torpedo tubes. The
U-19 class of 1912–13 saw the first
diesel engine installed in a German navy boat. At the start of World War I in 1914, Germany had 48 submarines of 13 classes in service or under construction. During that war the Imperial German Navy used
SM U-1 for training. Retired in 1919, it remains on display at the
Deutsches Museum in Munich.
[6]
World War I (1914–1918)
Main article: U-boat Campaign (World War I)
On 5 September 1914,
HMS Pathfinder was sunk by
SM U-21, the first ship to have been sunk by a submarine using a self-propelled torpedo. On
22 September, U-9 under the command of
Otto Weddigen sank the obsolete British warships
HMS Aboukir,
HMS Cressy and
HMS Hogue (the "
Live Bait Squadron") in a single hour.
In the
Gallipoli Campaign in early 1915 in the eastern Mediterranean, German U-boats, notably the
U-21, prevented close support of allied troops by 18
pre-Dreadnought battleships by sinking two of them.
[7]
For the first few months of the war, U-boat
anticommerce actions observed the
"prize rules" of the time, which governed the treatment of enemy civilian ships and their occupants. On 20 October 1914,
SM U-17sank the first merchant ship, the
SS Glitra, off Norway.
[8] 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, even potentially neutral ones, without warning.
In February 1915, a submarine
U-6 (
Lepsius) was rammed and both periscopes were destroyed off
Beachy Head by the collier
SS Thordis commanded by Captain John Bell RNR after firing a torpedo.
[9] On 7 May 1915,
SM U-20 sank the liner
RMS Lusitania. The sinking claimed 1,198 lives, 128 of them American civilians, and the attack of this unarmed civilian ship deeply shocked the
Allies. According to the ship's manifest,
Lusitania was carrying military cargo, though none of this information was relayed to the citizens of Britain and the United States who thought that the ship contained no ammunition or military weaponry whatsoever and it was an act of brutal murder. Munitions that it carried were thousands of crates full of ammunition for rifles, 3-inch artillery shells, and also various other standard ammunition used by infantry. The sinking of the
Lusitania was widely used as propaganda against the German Empire and caused greater support for the war effort. A widespread reaction in the U.S was not seen until the sinking of the ferry
SS Sussex. The sinking occurred in 1915 and the United States entered the war in 1917.
The initial U.S. response was to threaten to sever
diplomatic ties, which persuaded the Germans to issue the
Sussex pledge that reimposed 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 reapply prize rules. This, however, removed the effectiveness of the U-boat fleet, and the Germans consequently sought a decisive surface action, a strategy that 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 anticommerce 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.
U-Boot / Unterseeboot
Sinking of the Linda Blanche out of Liverpool by
SM U-21 (
Willy Stöwer)
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 on Germany in April 1917.
Unrestricted submarine warfare in early 1917 was initially very successful, sinking a major part of Britain-bound shipping. With the introduction of escorted convoys, shipping losses declined and in the end the German strategy failed to destroy sufficient Allied shipping. An armistice became effective on 11 November 1918. Of the surviving German submarines 14 U-boats were scuttled and 122 surrendered.
[10]
Of the 373 German submarines that had been built, 178 were lost by enemy action. Of these 41 were sunk by mines, 30 by depth charges and 13 by
Q-ships. 515 officers and 4894 enlisted men were killed. They sank 10 battleships, 18 cruisers and several smaller naval vessels. They further destroyed 5,708 merchant and fishing vessels for a total of 11,108,865 tons and the loss of about 15,000 sailors.
[11] The
Pour le Mérite, the highest decoration for gallantry for officers, was awarded to 29 U-boat commanders.
[12] 12 U-boat crewmen were decorated with the
Goldene Militär-Verdienst-Kreuz, the highest bravery award for non-commissioned officers and enlisted men.
[13] The most successful U-boat commanders of World War I were
Lothar von Arnauld de la Perière(189 merchant vessels and two gunboats with 446,708 tons), followed by
Walter Forstmann (149 ships with 391,607 tons), and
Max Valentiner (144 ships with 299,482 tons).
[14] Their records have never been surpassed by anyone in any later conflict so far.
Surrender of the fleet
Under the terms of armistice, all U-boats were to immediately surrender. Those in home waters sailed to the British submarine base at
Harwich. The entire process was done quickly and in the main without difficulty, after which the vessels were studied, then scrapped or given to Allied navies.
Interwar years (1919–1939)
The
Treaty of Versailles ending World War I signed at the
Paris Peace Conference in 1919 restricted the total tonnage of the German surface fleet. The treaty also restricted the independent tonnage of ships and forbade the construction of submarines. However, a submarine design office was set up in the Netherlands and a torpedo research program was started in Sweden. Before the start of World War II, Germany started building U-boats and training crews, labeling these activities as
"research" or concealing them using other covers. When this became known, the
Anglo-German Naval Agreement limited Germany to parity with Britain in submarines. When World War II started, Germany already had 65 U-boats, with 21 of those at sea, ready for war.
[16]
World War II (1939–1945)
Main article: Battle of the Atlantic
During
World War II, U-boat warfare was the major component of the
Battle of the Atlantic, which began in 1939 and ended with Germany's surrender in 1945. The Armistice of November 11th, 1918 ending
World War I had scuttled most of the old
Imperial German Navy and the subsequent
Treaty of Versailles of 1919 limited the surface navy of Germany's new
Weimar Republic to only six
battleships (of less than 10,000 tons each), six
cruisers, and 12
destroyers. To compensate, Germany's new navy, the
Kriegsmarine, developed the largest submarine fleet going into World War II.
[17] British Prime Minister
Winston Churchill later wrote
"The only thing that really frightened me during the war was the U-boat peril."
In the early stages of the war the U-boats were extremely effective in destroying
Allied shipping due to the large gap in mid-Atlantic air cover. Cross-Atlantic trade in war supplies and food was extensive and critical for Britain's survival. The continuous action surrounding British shipping became known as the
Battle of the Atlantic, as the British developed technical defences such as
ASDIC and
radar, and the German U-boats responded by hunting in what were called "
wolfpacks" where multiple submarines would stay close together, making it easier for them to sink a specific target. Britain's vulnerable shipping situation existed until 1942, when the tides changed as the U.S. merchant marine and Navy entered the war, drastically increasing the amount of tonnage of supplies sent across the Atlantic. The combination of increased tonnage and increased naval protection of shipping convoys made it much more difficult for U-boats to make a significant dent in British shipping. Once the United States entered the war, U-boats ranged 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. The
U.S. military engaged in various tactics against German incursions in the
Americas; these included military surveillance of foreign nations in Latin America, particularly in the Caribbean, to deter any local governments from supplying German U-boats.
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 more ship-like hull design reflects the fact that these were primarily surface vessels that could submerge when necessary. This contrasts with the cylindrical profile of modern
nuclear submarines, which are more hydrodynamic underwater (where they spend the majority of their time), but less stable on the surface. While U-boats were faster on the surface than submerged, the opposite is generally true of modern submarines. 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 tactics, which included convoys, was referred to by German submariners as "
die glückliche Zeit" or the
First Happy Time.
[18]
Torpedoes
The U-boats' main weapon was the
torpedo, though
mines and
deck guns (while surfaced) were also used. By the end of the war, almost 3,000 Allied ships (175 warships; 2,825 merchant ships) were sunk by U-boat torpedoes.
[19] Early German World War II torpedoes were straight runners, as opposed to the homing and pattern-running torpedoes that were fielded later in the war. They were fitted with one of two types of pistol triggers: impact, which detonated the warhead upon contact with a solid object, and
magnetic, which detonated upon sensing a change in the magnetic field within a few meters.
One of the most effective uses of magnetic pistols would be to set the torpedo's depth to just beneath the keel of the target. The explosion under the target's keel would create a
detonationshock wave, which could cause a ship's hull to rupture under the concussive water pressure. In this way, even large or heavily armored ships could be sunk or disabled with a single, well-placed hit.
Initially the depth-keeping equipment and magnetic and contact exploders were notoriously unreliable. During the first eight months of the war torpedoes often ran at an improper depth, detonated prematurely, or failed to explode altogether—sometimes bouncing harmlessly off the hull of the target ship. This was most evident in
Operation Weserübung, the invasion of Norway, where various skilled U-boat commanders failed to inflict damage on British transports and warships because of faulty torpedoes. The faults were largely due to a lack of testing. The magnetic detonator was sensitive to mechanical oscillations during the torpedo run, and to fluctuations in the Earth's magnetic field at high latitudes. These early magnetic detonators were eventually phased out, and the depth-keeping problem was solved by early 1942 with improved technology.
[20]
Later in the war, Germany developed an acoustic homing torpedo, the
G7/T5. It was primarily designed to combat convoy escorts. The acoustic torpedo was designed to run straight to an arming distance of 400 m and then turn toward the loudest noise detected. This sometimes ended up being the U-boat itself; at least two submarines may have been sunk by their own homing torpedoes. Additionally, these torpedoes were found to be only effective against ships moving at greater than 15 knots (28 km/h). The Allies countered acoustic torpedoes with noisemaker decoys such as
Foxer,
FXR,
CAT and
Fanfare. The Germans, in turn, countered this by introducing newer and upgraded versions of the acoustic torpedoes, like the late-war
G7es, and the
T11. However, the T11 did not see active service.
[21]
U-boats also adopted several types of "pattern-running" torpedoes that ran straight out 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 if the weapon missed its primary target.
U-boat developments
During World War II, the
Kriegsmarine produced many different types of U-boats as technology evolved. Most notable is the Type VII, known as the
"workhorse" of the fleet, which was by far the most-produced type, and the Type IX boats, an enlarged VII designed for long-range patrols, some travelling as far as Japan and the east coast of the United States.
Oil painting of a
Kriegsmarine U-boat, by
Augusto Ferrer-Dalmau
With the increasing sophistication of Allied detection and subsequent losses, German designers began to fully realise the potential for a truly submerged boat. The
Type XXI "
Elektroboot" was designed to favor submerged performance, both for combat effectiveness and survival. It was the first true submersible. The Type XXI featured an evolutionary design that combined several different strands of the U-Boat development program, most notably from the Walter U-boats, the
Type XVII, which featured an unsuccessful yet revolutionary
hydrogen peroxideair-independentpropellant system. These boats featured a streamlined hull design, which formed the basis of the later
USS Nautilus nuclear submarine, and was adapted for use with more conventional propulsion systems. The larger hull design allowed for a greatly increased battery capacity, which enabled the XXI to cruise submerged for longer periods and reach unprecedented submerged speeds for the time. Waste disposal was a problem when the U-boats spent extended periods without surfacing, as it is today.
Throughout the war, an
arms race evolved between the Allies and the
Kriegsmarine, especially in detection and counterdetection.
Sonar (ASDIC in Britain) allowed Allied warships to detect submerged U-boats (and vice versa) beyond visual range, but was not effective against a surfaced vessel; thus, early in the war, a U-boat at night or in bad weather was actually safer on the surface. Advancements in
radar became particularly deadly for the U-boat crews, especially once aircraft-mounted units were developed. As a countermeasure, U-boats were fitted with radar warning receivers, to give them ample time to dive before the enemy closed in, as well as more anti aircraft guns. However, by early to mid-1943, the Allies switched to
centimetric radar (unknown to Germany), which rendered the radar detectors ineffective. U-boat radar systems were also developed, but many captains chose not to use them for fear of broadcasting their position to enemy patrols and lack of sufficient electronic countermeasures.
Early on, the Germans experimented with the idea of the
Schnorchel(snorkel) from captured Dutch submarines, but saw no need for them until rather late in the war. The
Schnorchel was a retractable pipe that supplied air to the diesel engines while submerged at
periscope depth, allowing the boats to cruise and recharge their batteries while maintaining a degree of stealth. It was far from a perfect solution, however. Problems occurred with the device's valve sticking shut or closing as it dunked in rough weather; since the system used the entire pressure hull as a buffer, the diesels would instantaneously suck huge volumes of air from the boat's compartments, and the crew often suffered painful ear injuries. Speed was limited to 8 knots (15 km/h), lest the device snap from stress. The
Schnorchel also had the effect of making the boat essentially noisy and deaf in sonar terms. Finally, Allied radar eventually became sufficiently advanced that the
Schnorchel mast could be detected beyond visual range.
Several other pioneering innovations included acoustic- and electro-absorbent coatings to make them less of an ASDIC or RADAR target. The Germans also developed active countermeasures such as facilities to release artificial chemical bubble-making decoys, known as
Bold, after the mythical
kobold.
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U-boat - Wikipedia08 May 2019.
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