In September 1918. the Board of Trade introduced an identity card, with photograph for all seamen working in the British Merchant Marine, together with a matching central card index (CR 10 cards).
This central index contains 300,000 cards which include, for each seaman, his personal details, photo, and foreign voyage starts. Seamen in the home trade were included, but their voyages were not recorded. The system operated until December 1921.
David Snook has developed an online searchable database of 23,000 Irish merchant seamen extracted and transcribed from the CR 10 cards which are now held at Southampton Civic Archives.