WITH a vertical take‐off aircraft like the Hawker Siddeley Harrier, the only ground attack/ reconnaissance jet V/S.T.O.L. weapons system in operational service today, the air intakes have a vital influence on design and performance. At lift‐off and landing they need to absorb an exceptionally large flow of air with minimum loss. This demands a relatively large intake, which in turn increases the difficulty of keeping down drag during high speed flight. These design problems had to be met whilst providing also the ability to accept violent manoeuvring throughout all phases of the operational envelope.