Salisbury-class frigate

The Type 61 Salisbury class were a class of British aircraft direction (or radar picket) frigates built for the Royal Navy.

They were related to the Type 41 Leopard class frigates, but with reduced armament to make way for more aircraft direction equipment. Unlike the Battle class AD conversions, the primary role of the Type 61 was not operations with fast carrier groups for which their diesel powered cruising engines, increasingly lacked the speed. The role of the Type 61 was as a seaworthy air ocean surveillance ship and air control ship supporting Suez ( for which they were too late) type amphibious operations and air strikes.

The equipment fitted to the Type 61s was essentially that of second line aircraft carriers and ambhibious helicopter carriers. While the frontline carriers (eg Eagle, Hermes and Victorious) carried the 3D bulky 984 radar and the ability to analyse and prioritise 24 to 100 air targets, the second line carriers (Ark Royal, Centaur, Bulwark, Albion) and the Type 61 AD frigates carried initially 960 (rapidly updated to 965) radar for AW and 982 radar for a degree of 3D cover and better air control over land.

By the late 1960s the decision to phase out the carriers and other factors were making the 984 unsustainable. Hermes and Victorious were too small to carry secondary surveillance or backup radar; 984 was becoming more difficult to maintain and not reliable, and Victorious and Hermes essentially had a capacity for only 25 second generation fighter and bombers and ASW helicopters, which was of limited value.

Therefore a new radar, 985, superior as a radar to 984 and 965 was developed to use the 982 antenna and fitted in the late 1960s to what would be the last conventional carriers, Ark Royal and Bulwark, and the Type 61 escorts.

However the 985 system did not have the analysis and prioritising capabilities of the 984 system and the Type 61s lacked the computer processing capability to properly process the data or really effectively operate with the Ark.

Construction Programme
Three further ships of the class were planned. Two of these were cancelled under the 1957 Defence Review, and the third (Coventry) was suspended. It was hoped to order Coventry in 1961, but in the event it was decided to order a Leander class frigate that became HMS Penelope.