[1] The ship was originally ordered from William Pickersgill & Sons Ltd. of South Bank, Middlesbrough, on 25 January 1943 as the Loch-class frigate Loch Mochrum.

However the contract was then changed, and the ship was laid down as Admiralty Job Number 4813 on 30 November 1944 to a revised design as a Bay-class frigate, and launched on 24 September 1945 as Pegwell Bay.

No main armaments were fitted and changes were made to provide additional accommodation and offices for hydrographic work.

[2] In 1955 Cook began to carry out trials of the Decca Two Range Survey System, which fixed the ship's position by radio signals from two shore stations.

[1] In March 1957 she sailed to the Pacific, via the Azores, the West Indies, and Panama Canal, to observe the first British thermonuclear bomb test, code-named "Operation Grapple", on 15 May.

In November she sailed to Singapore, where her captain was court-martialed and found guilty of hazarding and stranding his ship.