FD was used for Ford. An aircraft at Ford carrying the letter J would be a visitor – long or short stay would depend on circumstances. The single letter codes belonged to the carriers – hence not EG for Eagle. The two letter codes belonged to the shore bases and other aircraft-operating ships (for example, EN was Engadine).

The Air Britain book The Squadrons of the Fleet Air Arm devotes 27 pages of very small print to the variations of such codes. 17 of these are devoted to post-war examples in three periods, but the summary above applies to all.