Combined Operations Headquarters worked closely with several intelligence organisations to plan the raid. The Naval Intelligence Division compiled information from a variety of sources. A detailed plan of the town of St Nazaire was provided by the Secret Intelligence Service, and information on the coastal artillery nearby was sourced from the War Office's Military Intelligence branch. Intelligence about the dock itself came from pre-war technical journals. The Naval Operational Intelligence Centre selected the route and timing for the raid based on intelligence about the location of minefields and German recognition signals sourced from Enigma decryptions and knowledge of Luftwaffe patrols compiled by the Air Ministry's Air Intelligence Branch. When all the plans had been pulled together and the timing worked out, the main part of the raid was expected to last no longer than two hours. The commandos and crew from "Campbeltown" were to board the motor launches at the Old Mole jetty and then return to base.