Detection still depends on lookouts, with both the lookout's height and the target's altitude affecting visibility. A high aircraft can be seen farther away than one approaching close to the sea. The 3-inch gun comparison gives about 75 square kilometres of coverage and a range just under 5 kilometres, assuming an unobstructed mounting able to fire all round. The Mark II pom-pom is assigned 3.8 square kilometres. A practical altitude of 15,000 feet is distinguished from greater theoretical reach. Maximum altitude also depends on ammunition: the figures given are 23,500 feet with a 12-pound shell and 22,000 feet with a heavier 16-pound shell. Extra gun reach is of limited use when the crew cannot detect a target far enough away to exploit it.
Notable Point · 30:30-33:44
Gun coverage and visual detection in 1916
Compare the 3-inch gun and Mark II pom-pom while separating nominal weapon reach from what lookouts could see and engage.