By the end of WW2 only 15% of Royal Navy officers were regulars. Initially numbers were made up from the RNR - officers with Merchant Service qualifications - and the pre-war RNVR, volunteers who like the RNR had periodic training attachments to the RN. The RNR provided a number of commanding officers for corvettes and, later, frigates. The next tranche came from a register of pre-war yachtsmen, the RNV(S)R, who had no RN involvement but were screened to ensure they had sea experience. These were embodied and trained and sent forth mostly to serve in corvettes in the Battle of the Atlantic. Finally the Admiralty began training and commissioning ‘HO’s, ‘Hostilities Only’ ratings selected after six months sea service, who followed the yachtsmen to a training base in Lancing and Hove, HMS King Alfred. This provided nearly all the junior officers in the convoy escorts and in Coastal Forces and in Landing Craft, with some rising to ship and even squadron command. By the end of the war some had made commander and some were commanding submarines. The magic trick is that somehow the relatively small peacetime RN took all these people in and made them into functioning naval officers, as also the crowded mess decks turned thousands of civilians into matelots and proud members of the Andrew Miller. This book, by Brian Lavery of the National Maritime Museum, draws on official records and personal reminiscences, published and otherwise, to give us a pretty complete picture of ’temporary’ officers’ training and employment. He takes time to tell us what it was really like standing watch and watch in appalling weather for weeks on end in the Atlantic, or in the chaos of the D-Day beaches. Among others we meet Nicholas Monsarrat and the actors Peter Bull and Alec Guinness. Fleet Air Arm aircrew officers followed a different path and are outside the scope of this book as are some niche aspects of a navy in which maybe a million men and women served during WW2. But as a relatively comprehensive review of the officer recruitment, training and operational experience three almost non-straight-stripe navies I would give it five stars.