The next instalment of Sky News’ Prepared For War? series looks at the UK’s hallowed out air defence. The RAF has nine frontline fighter squadrons compared with 30 in operation near the end of the Cold War. In the Navy, only three of the six destroyers capable of shooting down ballistic missiles are in operation. And on land, only four of the six ground-based air defence systems that can take out jets and missiles are in the UK with two deployed overseas.