SM U-4 or U-IV was a U-3-class submarine or U-boat built for and operated by the Austro-Hungarian Navy (German: Kaiserliche und Königliche Kriegsmarine or German: K.u.K. Kriegsmarine) before and during the First World War. The submarine was built as part of a plan to evaluate foreign submarine designs, and was the second of two boats of the class built by Germaniawerft of Kiel, Germany.
U-4 was authorized in 1906, begun in March 1907, launched in November 1908, and towed from Kiel to Pola in April 1909. The double-hulled submarine was just under 139feet long and displaced between 240t300t, depending on whether surfaced or submerged. The design of the submarine had poor diving qualities and several modifications to U-4s diving planes and fins occurred in her first years in the Austro-Hungarian Navy. Her armament, as built, consisted of two bow torpedo tubes with a supply of three torpedoes, but was supplemented with a deck gun, the first of which was added in 1915.
The boat was commissioned into the Austro-Hungarian Navy in August 1909, and served as a training boat—sometimes making as many as ten cruises a month—through the beginning of the First World War in 1914. At the start of that conflict, she was one of only four operational submarines in the Austro-Hungarian Navy U-boat fleet. Over the first year of the war, U-4 made several unsuccessful attacks on warships and captured several smaller vessels as prizes. In July 1915, she scored what Conway's All the World's Fighting Ships 1906–1921 calls her greatest success when she torpedoed and sank the Italian armored cruiser, the largest ship hit by U-4 during the war.
In mid-May 1917, U-4 was a participant in a raid on the Otranto Barrage which precipitated the Battle of Otranto Straits. In a separate action that same month, U-4 sank her second largest ship, the Italian troopship Perseo. She scored her final success in July 1917 with the sinking of a French tug. In total, U-4 sank fifteen ships totaling and 7,345 tons. She survived the war as Austria-Hungary's longest serving submarine, was ceded to France as a war reparation, and scrapped in 1920.
U-4 was built as part of a plan by the Austro-Hungarian Navy to competitively evaluate foreign submarine designs from Simon Lake, Germaniawerft, and John Philip Holland.[1] The Austro-Hungarian Navy authorized the construction of U-4 (and sister ship, U-3) in 1906 by Germaniawerft of Kiel, Germany. U-4 was laid down on 12 March 1907 and launched on 20 November 1908.[2] After completion, she was towed via Gibraltar to Pola, where she arrived on 19 April 1909.
U-4s design was an improved version of Germaniawerft's design for the Imperial German Navy's first U-boat,, and featured a double hull with internal saddle tanks. The Germaniawerft engineers refined the design's hull shape through extensive model trials.
U-4 was 138feet long by 14feet abeam and had a draft of 12inchesft6inchesin (ftin). She displaced 240t surfaced and 300t submerged. She was armed with two bow 45cm (18inches) torpedo tubes, and was designed to carry up to three torpedoes.
After U-4s arrival at Pola in April 1909, she was commissioned into the Austro-Hungarian Navy on 29 August 1909 as SM U-4.[3] During the evaluation of the U-3 class conducted by the Navy, the class' poor diving and handling characteristics were noted. To alleviate the diving problems, U-4s fins were changed in size and shape several times, and eventually, the front diving planes were removed and a stationary stern flap was affixed to the hull.[4] U-4 served as a training boat between 1910 and 1914 and made as many as ten cruises per month in that capacity.[5]
At the beginning of World War I, she was one of only four operational submarines in the Austro-Hungarian Navy.[6] On 27 September 1914, U-4 began operating reconnaissance cruises out of the naval base at Cattaro under the command of Linienschiffsleutnant Hermann Jüstel. U-4 attacked the cruiser Waldeck-Rousseau on 17 October, but the French vessel escaped without serious damage.[7] In late November, U-4 seized the Albanian sailing vessel Fiore del Mar as a prize off Montenegro.[8] U-4 received her first radio set the following month.
U-4s next success was the capture of three Montenegrin boats on 19 February 1915. Rudolf Singule, who was to become U-4s most successful commander,[9] assumed command of the boat in April 1915.[10] Around the same time, the boat was equipped with a 3.7sp=usNaNsp=us quick firing (QF) deck gun. On 24 May, in the Gulf of Drin, U-4 unsuccessfully attacked an Italian, but on 9 June, Singule spotted the British cruiser escorting a convoy along the Montenegrin coast. Despite a screen of six destroyers, U-4 was able to torpedo Dublin off San Giovanni de Medua.[11] Twelve men on Dublin died in the attack,[12] but the cruiser made her way safely, albeit damaged, back to port.
On 18 July, U-4 chanced upon an Italian squadron of ships shelling the railroads at Dubrovnik. Singule selected the Italian armored cruiser as a target and torpedoed her.[13]