Merchant aircraft carrier

A merchant aircraft carrier (also known as a MAC) was a limited purpose aircraft carrier built on a British hull designed for bulk grain ships and oil tankers. This was adapted by adding a flight deck enabling it to operate anti-submarine aircraft in support of Allied convoys during the Battle of the Atlantic during World War II.

Despite their quasi-military function, MACs retained their mercantile status, continued to carry cargo and operated under civilian command. MACs began entering service in May 1943 and although originally intended as an interim measure pending the introduction of escort carriers, they remained operational until the end of the war in Europe.

In 1940, Captain M. S. Slattery RN, Director of Air Material at the Admiralty, proposed a scheme for converting merchant ships into aircraft carriers as a follow-up to the CAM ship project. Slattery proposed fitting a flight deck equipped with two arrester wires and a safety barrier onto an existing merchant ship hull. The resulting 'auxiliary fighter carrier' would be capable of operating six Hurricane fighters while retaining its cargo-carrying ability. The stumbling block for Slattery's proposal turned out to be objections from the Ministry of Supply that combining the merchant and aircraft carrier roles would be too complicated. While this would turn out to be over-stated, it seems to have had the effect of diverting attention away from the idea of hybrid merchant-warships towards the alternative of converting merchant ships into fully-fledged warships designated 'auxiliary aircraft carriers', the first of which, converted from the captured German cargo ship Hannover, entered service as Empire Audacity (later HMS Audacity) in June 1941.

The hybrid concept re-emerged early in 1942 when, in the face of mounting losses from U-boat attacks, it became apparent that escort carriers building in the US could not be delivered quickly enough in the numbers required. Various people have been credited with re-inventing the idea, including Captain B. B. Schofield RN, Director Trade Division, and John Lamb, Marine Technical Manager of the Anglo-Saxon Petroleum Company.Sir James Lithgow, Controller of Merchant Shipbuilding and Repair and joint-owner of Lithgows Ltd, the Clyde-based shipbuilders, also helped overcome Admiralty reservations about MACs. Lithgow is said to have sketched a rough design for one on the back of an envelope and offered to convert two ships about to be built at his family's shipyard on condition that "I am not interfered with by the Admiralty". While the timing of Lithgow's possibly apocryphal intervention is uncertain, his deputy, Sir Amos Ayre, the Director of Merchant Shipbuilding, was certainly discussing the requirements for MACs by May 1942. Ayre himself credits Sir Douglas Thomson of Ben Line and the Ministry of War Transport with having first suggested the idea.

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