World Warr II stimulated another divergence in the aeroplane’s development. The few biplanes surviving in front-line units quickly disappeared, while many of the advances in late-1930s civil aviation were hurriedly adapted for military use. Armament had improved little in the interwar period, but heavily-armed fighters soon predominated. High-speed bombers required efficient, power-operated turrets for their defensive weaponry, and bomb capacities and range also increased. Flying boats again proved valuable for patrol and anti-submarine work. Ground-attack, a role that had evolved at the end of World War I, assumed greater significance as control of airspace over a battlefield became vital. The aircraft carrier played a prominent part in the war
at sea. Following initial experiments in the 1930s, the jet engine became a practical proposition and the first jet-propelled fighters and bombers appeared towards the end of the war.