The HMS Dreadnought was the first battleship to use steam turbines in place of the older reciprocating triple-expansion steam engines. The refitted 1915 design was assigned to the 1st Division Home Fleet and served with the 4th Battle Squadron in the North Sea during the first two years of WWI and was the only battleship ever to sink a submarine when it did so in 1915. During the 1915 re-fit, a pair of QF 6-pdr Hotchkiss AA guns on high-angle mountings were mounted on the quarterdeck.