Automatic 6-inch guns are described as disappointing air-defence weapons when their reach is compared with the 5-inch/54. The 6-inch Mark N5 example is assigned a maximum anti-aircraft range of 25,000 yards and a ceiling of 40,000 feet. The 5-inch/54 Mark 16 is given an effective range of 19,000 yards, a maximum horizontal reach of about 23.6 kilometres and a ceiling of 51,600 feet. Those figures allow the smaller weapon to outrange the particular 6-inch gun in the comparison. Its theoretical horizontal coverage of 1,763.26 square kilometres is illustrated as larger than Greater London and more than twice New York City's area. Cooperation with the Americans also runs through these programmes: the 6-inch effort is described as semi-joint, and the 3-inch programme as joint.
Notable Point · 1:16:12-1:22:05
Why automatic 6-inch guns disappointed in air defence
The quoted performance of the 5-inch/54 explains why a larger automatic 6-inch gun did not necessarily offer a better anti-aircraft envelope.