Hornbeam.
This was the cold war spy guide issued to some vessel captains in the British Merchant Navy and fishing fleets. Operation Hornbeam was a secret project aimed at gathering intelligence on the specification and location of enemy (Communist) vessels from countries such as USSR, Vietnam, Romania, Poland, China, Hungry, German Democratic Republic, Czechoslovakia, Korea, Cuba, Albania, Bulgaria etc. The document runs to over 100 pages and includes numerous ship profiles, guide to identifying electronic communications equipment, lists of vessels, coloured pages of stack markings and ensigns and of course instructions on what to record and report back.
Paul Hood. + WSS Tyneside Branch Hon Sec.