Tribal-class frigate

The Tribal class, also known as the Type 81 frigates, was a class of seven ships built for the Royal Navy in the early 1960s. They were ordered and built as sloops for duties like those of the improved Black Swan sloops and Loch-class frigates in the Persian Gulf, with colonial gunboat work in the Middle East in mind, and were self-contained warships with air conditioning and bunk accommodation for tropical service. They were the first Royal Navy class designed from the start to operate a helicopter and the first small escorts to carry a long-range air search radar, the Type 965. Machinery was the combined steam and gas arrangement known as COSAG, a steam turbine plant with a gas turbine boost that let the ships leave port almost at once, driving a single shaft that limited manoeuvrability. They carried two 4.5 inch guns and received Seacat missiles in the 1970s. In the mid-1960s the seven ships were reclassified as general-purpose frigates, and Yarrow was involved in designing and building the class.