Merchant aircraft carrier

MAC ships entered service from May 1943 when they began to supplement and supplant escort carriers, and remained operational until the end of the war in Europe.

[2][3] Slattery proposed fitting a flight deck equipped with two arrester wires and a safety barrier onto an existing merchant ship hull.

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.

[3][4] 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.

[9] 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 MAC ships by May 1942.

[3][11] As the U-boat situation worsened, however, such concerns were out-weighed by the urgent need to provide convoy air support, and once it was accepted that the grain ship variant at least could be made to work, the Admiralty became more enthusiastic about the project.

By September 1942, the Admiralty was asking for "about 50" MAC ships to be made available, to allow one to be included in every North Atlantic convoy and in October the requirement was set at 52.

[12][13] This ambitious target had been scaled back to 40 by the time the MAC ship project was formally endorsed by the War Cabinet in October 1942, but it was apparent that even this reduced number could not be produced sufficiently quickly without American help.

The initial response was not helpful with Norway insisting on financial arrangements that War Transport officials described as "wholly unreasonable as between allies", but although these were later ameliorated, the proposal eventually foundered because the design effort was judged too much for what would have been a one-off conversion.

The Admiralty's preference was to operate them as regular warships but it soon became clear that there were not enough personnel available to man them to naval standards without causing serious shortfalls in other areas, in particular the large numbers of escort carriers that would soon arrive.

The risk to MAC ship crews was considered so great that it was explicitly put before the War Cabinet: The greater the effect of air action on the U-boat campaign, the more the enemy may be tempted to try to damage the morale of M.A.C.

The Foreign Office reluctantly agreed that the MAC ships would have to operate under the Red Ensign, provided that the merchant seamen and their unions were made aware of the risks involved, and that every possible precaution would be taken to ensure that the men did not fall into enemy hands.

[30] The new-build grain carrier MAC ships were based on the Ministry of War Transport's standard tramp hull which could just accommodate the Admiralty's revised requirement for a flight deck of not less than 390 feet (120 m) length and 62 ft (19 m) breadth.

The standard design used for the new-build tankers enabled a longer flight deck of approximately 460 ft (140 m) with minor variations between individual ships.

[7] The most obvious modification was the flight deck and its supporting structure which was arranged in sections (three on the grain ships; four in the case of tankers) with expansion joints between each.

[7] It was impracticable to fit tanker MAC ships with a hangar as this would have entailed very extensive structural alterations and a significant reduction in cargo capacity.

Hinged side screens or 'palisades' were fitted around the aft end of the flight deck to provide weather protection for parked aircraft but with only limited effect.

[31] The net result of the modifications was a reduction in cargo capacity of about 10% in the case of the tankers, but almost 30% for the grain ships, the higher figure on account of the space taken up by the hangar.

[7] Delays arose through a variety of reasons, including labour relations and conflicting priorities in the shipyards, but the supply of arrester gear which was also in high demand for the escort carrier programme was a particular bottleneck that limited the rate at which MAC ships could be completed.

[37] Although the most distinctive feature of MACs is their aircraft carrier function, they were conceived at a time when a shortage of shipping capacity threatened to undermine the Allied invasion of North Africa and beyond, and careful planning was needed to maximise their military effectiveness with as little detriment as possible to the carriage of cargo.

The Director of Trade Division, who had overall responsibility for co-ordination within the Admiralty, envisaged forming a new headquarters organisation to oversee MAC ship aviation.

[43][44] However, when the escort carrier HMS Dasher exploded and sank in March 1943 it freed up a squadron's-worth of Swordfish aircraft and in June, just after Empire MacAlpine entered service, it was announced that No.

836 Naval Air Squadron (NAS) was to relocate from Machrihanish to Belfast in Northern Ireland with nine aircraft as a core for the MAC ships, in addition to providing a common pool for the escort carriers.

[49][50][51] Lieutenant (later Captain) Eric "Winkle" Brown made a trial landing of a Martlet fighter onto Amastra in October 1943 when the use of MACs in the Pacific was being briefly considered.

To comply with the Board of Trade regulations, all naval and military personnel were signed onto the ship's Articles as supernumerary crew members, for which they received a nominal payment of one shilling per month and the more tangible reward of one can of beer per day.

[31][51] By the time the MAC ships entered service the Battle of the Atlantic had already swung permanently in the Allies' favour through a variety of converging factors.

[48] Nevertheless, according to the official Naval Staff History: It is sometimes claimed that MAC ships enjoyed a near-perfect record in preventing U-boat attacks.

The possibility of using them in the Pacific as aircraft carriers or fleet oilers had been considered earlier but rejected on the grounds of cost-effectiveness and in September/October 1944, Acavus, Amastra, Ancylus and Rapana were taken out of service for reinstatement as conventional merchant ships at an estimated cost to the Government of £40,000 each.