"Iron Duke" was the first British battleship to be mounted with anti-aircraft weaponry. In 1914, two 3 in (7.62 cm) QF guns were fitted to the aft superstructure, primarily to defend against German airships. The guns fired between 12–14 rounds per minute, and were expected to fire approximately 1,250 shells before replacement or repair was necessary. The shells fired were 12.5 lb (5.67 kg) with a high-explosive warhead. They were manually operated, and had a maximum effective ceiling of 23,500 ft (7,160 m).