SM U-4 (Austria-Hungary)

SM U-4 (Austria-Hungary)

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 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 139 feet (42 m) long and displaced between 240 and 300 tonnes (260 and 330 short tons), depending on whether surfaced or submerged. The design of the submarine had poor diving qualities and several modifications to U-4's 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 Giuseppe Garibaldi, 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 twelve ships totaling over 18,000 gross register tons (GRT). She survived the war as Austria-Hungary's longest serving submarine, was ceded to France as a war reparation, and scrapped in 1920.