These ships were the Royal Navy's first privately designed warships for many years. They were also the first design to enter service with the Royal Navy to be solely powered by gas-turbine engines, with two Rolls-Royce Tynes for cruising and two Rolls-Royce Olympus for high speeds arranged in a combined gas or gas (COGOG) arrangement. The design made use of large amounts of aluminium alloy in the superstructure to reduce the topweight. Worries later surfaced about its resilience to fire, particularly following a major fire on "Amazon" in 1977 during which aluminium ladders distorted, preventing fire-fighting teams from reaching the blaze, and its ability to withstand blast damage. Later warships reverted to using steel.