[3] Ships based at Ferret were under the operational control of Western Approaches Command, located in Plymouth for the early part of the war.

[1] The organisational function of Ferret was to form Escort Groups of the warships based there, mostly small destroyers, frigates, corvettes and armed trawlers.

By 1942 this system had been extended to handle the accounts of Royal Navy ships at St John's and Argentia naval bases in Newfoundland.

[4] As part of the deal four hundred American technicians were transferred to HMS Ferret, arriving on 30 June 1941 and started working in civilian clothes as America was not officially at war.

[4] After the end of the war, large numbers of captured German U-boats were surrendered to British forces on the Scottish and Irish coasts and were brought to Lisahally.

There was a debate over the future of the base, but the Admiralty decided to retain the property but to convert it into a proper school for anti-submarine warfare training.

Professor J. W. Blake, in his 1956 book Northern Ireland and the Second World War summarised the importance of the work of HMS Ferret: "Londonderry held the key to victory in the Atlantic.

By that critical Spring (1943) when battle for the security of our Atlantic lifelines finally turned our way, Londonderry was the most important escort base in the north-western approaches.