due to hostilities. US submarines sank 1,560 enemy vessels, a total tonnage of 5.3 million tons (55% of the total sunk). The Royal Navy Submarine Service was used primarily in the classic Axis blockade. Its major operating areas were around Norway, in the Mediterranean (against the Axis supply routes to North Africa), and in the Far East. In that war, British submarines sank 2 million tons of enemy shipping and 57 major warships, the latter including 35 submarines. Among these is the only documented instance of a submarine sinking another submarine while both were submerged. This occurred when engaged ; the Venturer crew manually computed a successful firing solution against a three-dimensionally maneuvering target using techniques which became the basis of modern torpedo computer targeting systems. Seventy-four British submarines were lost, the majority, forty-two, in the Mediterranean. Cold-War military models The first launch of a cruise missile (SSM-N-8 Regulus) from a submarine occurred in July 1953, from the deck of , a World War II fleet boat modified to carry the missile with a nuclear warhead. Tunny and its sister boat, , were the United States' first nuclear deterrent patrol submarines. In the 1950s, nuclear power partially replaced diesel–electric propulsion. Equipment was also developed to extract oxygen from sea water. These two innovations gave submarines the ability to remain submerged for weeks or months. Most of the naval submarines built since that time in the US, the Soviet Union/Russian Federation, Britain, and France have been powered by nuclear reactors. In 1959–1960, the first ballistic missile submarines were put into service by both the United States () and the Soviet Union () as part of the Cold War nuclear deterrent strategy. During the Cold War, the US and the Soviet Union maintained large submarine fleets that engaged in cat-and-mouse games. The Soviet Union lost at least four submarines during this period: was lost in 1968 (a part of which the CIA retrieved from the ocean floor with the Howard Hughes-designed ship Glomar Explorer), in 1970, in 1986, and in 1989 (which held a depth record among military submarines—). Many other Soviet subs, such as (the first Soviet nuclear submarine, and the first Soviet sub to reach the North Pole) were badly damaged by fire or radiation leaks. The US lost two nuclear submarines during this time: due to equipment failure during a test dive while at its operational limit, and due