The Acorn class (officially redesignated the H class in 1913) was a class of twenty destroyers of the Royal Navy all built under the 1909-1910 Programme, and completed between 1910 and 1911. The Acorns served during World War I. After the coal-burning Beagle or G class of 1909, the Acorns marked a return to oil-firing as pioneered in the Tribal or F class of 1905 and HMS Swift of 1907. This change allowed a generally smaller vessel than the Beagles even with an increase in armament. Three ships were lost in wartime service.