diving trial at sea on 6 April 1902. Although the design had been purchased entirely from the US company, the actual design used was an untested improvement to the original Holland design using a new petrol engine. These types of submarines were first used during the Russo-Japanese War of 1904–05. Due to the blockade at Port Arthur, the Russians sent their submarines to Vladivostok, where by 1 January 1905 there were seven boats, enough to create the world's first "operational submarine fleet". The new submarine fleet began patrols on 14 February, usually lasting for about 24 hours each. The first confrontation with Japanese warships occurred on 29 April 1905 when the Russian submarine Som was fired upon by Japanese torpedo boats, but then withdrew. World War I Military submarines first made a significant impact in World War I. Forces such as the U-boats of Germany saw action in the First Battle of the Atlantic, and were responsible for sinking , which was sunk as a result of unrestricted submarine warfare and is often cited among the reasons for the entry of the United States into the war. At the outbreak of the war, Germany had only twenty submarines immediately available for combat, although these included vessels of the diesel-engined U-19 class, which had a sufficient range of and speed of to allow them to operate effectively around the entire British coast., By contrast, the Royal Navy had a total of 74 submarines, though of mixed effectiveness. In August 1914, a flotilla of ten U-boats sailed from their base in Heligoland to attack Royal Navy warships in the North Sea in the first submarine war patrol in history. The U-boats' ability to function as practical war machines relied on new tactics, their numbers, and submarine technologies such as combination diesel–electric power system developed in the preceding years. More submersibles than true submarines, U-boats operated primarily on the surface using regular engines, submerging occasionally to attack under battery power. They were roughly triangular in cross-section, with a distinct keel to control rolling while surfaced, and a distinct bow. During World War I more than 5,000 Allied ships were sunk by U-boats. The British responded to the German developments in submarine technology with the creation of the K-class submarines. However, these submarines were notoriously dangerous to operate due to their various design flaws and poor maneuverability. World War II During World War II,