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Merchant aircraft carrier

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mv Rapana, an oil tanker converted into a Merchant Aircraft Carrier (MAC). MACs were introduced to provide air cover for convoys until sufficient escort carriers became available to replace them.

Merchant aircraft carrier (MAC) ships were bulk grain ships and oil tankers fitted with flight decks enabling them to operate anti-submarine aircraft in support of convoys during the Battle of the Atlantic. 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.[1][2]

Development

Various schemes for converting merchant ships into aircraft carriers had been suggested to the Admiralty as far back as the First World War but none seem to have been taken up.[3] In 1940, Captain M S Slattery RN, Director of Air Material at the Admiralty, resurrected the idea as a follow-up to the CAM Ship project.[4][5] 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.[5] 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.[5][6]

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.[7] Various people have been credited with re-inventing the idea, including Captain B B Schofield RN, Director Trade Division, and Mr John Lamb, Marine Technical Manager of the Anglo-Saxon Petroleum Company.[8][9][1][10] 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".[1] 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.[11] Ayre himself credits Sir Douglas Thomson of Ben Line and the Ministry of War Transport with having first suggested the idea.[9]

There was some initial resistance to the MAC concept, in particular through concerns about operating aircraft from short, relatively slow ships. The Admiralty considered that a flight deck length of 460 ft. was needed for safe take-offs and landings and a speed of 15 kts. to provide a sufficient margin over convoy speeds and they were especially doubtful that tankers, with their low freeboards and volatile cargoes, could be utilised.[5][12] 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' MACs to be made available, to allow one to be included in every North Atlantic convoy and in October the requirement was set at 52 .[13][14] This ambitious target had been scaled back to 40 by the time the MAC 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.[15][16] The US was therefore asked to begin construction of 30 MACs to be delivered during the first half of 1943, but a Navy Department committee specially formed to consider the request turned it down because of concerns about the experimental nature of the ships.[17][18] In the event, all the MACs were built and/or converted in British shipyards.

Conversion programme

The first two MACs were ordered in June 1942 from the Burntisland Shipbuilding Company on the Firth of Forth and William Denny & Brothers of Dumbarton. These ships, which were not strictly conversions but brand-new grain ships that had not yet been laid down, would eventually enter service as Empire MacAlpine and Empire MacAndrew respectively.[19] Empire MacAlpine was launched on 23 December 1942 and completed more-or-less on schedule on 21 April 1943. Five more new-build grain ships, Empire MacAndrew, Empire MacRae, Empire MacCallum, Empire MacKendrick and Empire MacDermott followed at approximately two-month intervals, Empire MacDermott entering service in March 1944.

By late September 1942 it was finally agreed that tanker-MACs could be operated safely subject to various limitations about the cargoes they would be allowed to carry. Four new-build tankers were scheduled for conversion but work on these did not start until May 1943. Empire MacKay entered service in October 1943, followed at intervals by Empire MacCabe, Empire MacMahon and Empire MacColl in November 1943. Additional hulls were still needed, however, and it was decided that existing tankers would have to be withdrawn from trade. The most efficient way to approach the task of converting these was to select ships of similar design and, at the beginning of 1943, the Anglo-Saxon Petroleum Company, which had actively promoted the MAC concept, offered up its entire fleet of British-registered 'Triple Twelve' tankers (sometimes referred to as the Rapana class) for government charter.[20][21][22][9]

The desirability of converting foreign-owned tankers was also considered and in January 1943 the Ministry of War Transport asked the Norwegian government-in-exile if the modern Norwegian tanker B.P. Newton could be converted to a MAC under British command. 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.[23][24] At about the same time however, a further three tankers of the same class as the Anglo-Saxon 'Triple Twelves' were identified operating under Dutch registry (Anglo-Saxon Petroleum was a subsidiary of Royal Dutch Shell). The Netherlands authorities approved the British request but on condition that the ships, as MACs, would fly the Dutch flag and be under Dutch civilian command to which the Admiralty, citing potential language difficulties, only reluctantly agreed.[25][26] In the event, only two of the Dutch ships were taken up as MACs but these, Gadila and Macoma, crewed entirely by Dutch merchant seamen and with aircraft flights drawn from the Royal Netherlands Navy-manned 860 Naval Air Squadron would have the distinction of becoming the Netherlands' first aircraft carriers.

Civilian status

Despite their military appearance and combatant function, MACs were civilian ships that did not appear in the Navy List nor were they commanded by commissioned officers: this unusual status is one of their defining characteristics. The hybrid nature of the MACs raised from the outset the question of whether they would be commissioned warships like the new escort carriers, or if they would operate as merchant ships under the Red Ensign like the earlier CAM ships. 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.[27] The Admiralty and Ministry of War Transport therefore agreed that the MACs would be civilian-manned. They would operate under the aegis of the Ministry of War Transport, with day-to-day management falling to their owners or allotted shipping companies, while control of military aspects would fall to the Admiralty, with a new section (the Trade Division DEMS Air Section) specially set up to act as co-ordinating authority.[28] Serious reservations about the proposed civilian status were raised, however, by Foreign Office officials, who were concerned that the ships would be de-facto warships under international law but, without the protection afforded by the 1907 Hague Convention which applied only to members of the armed forces, their civilian crews would be liable to be treated as unlawful combatants, or francs-tireurs.[29] The potential for such action had been clearly demonstrated by the execution in 1916 of Captain Fryatt, for attempting to ram a U-boat with his cross-Channel ferry. The risk to MAC 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. crews by court martialling and shooting any Merchant Service personnel they may capture from such ships."[30]

The War Cabinet ordered a review of the situation but the manning difficulties could not be resolved. The Foreign Office reluctantly agreed that the MACs 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.[31] In the event, there is little to suggest that the MACs' crews were ever formally notified that they might be at special risk. There is evidence, however, that the authorities remained sensitive about the status of MAC ships which were specifically excluded from the publicity that was arranged for other 'special service' merchant ships, eg rescue ships.[32] As late as September 1944, masters were reminded to point out to their crews the need to maintain secrecy about the MACs' operations and functions.[33]

Ship details

The new-build grain ship MACs 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 ft length and 62 ft. breadth: they were eventually built with flight decks of between 413 ft. and 424 ft. The standard design used for the new-build tankers enabled a longer flight deck of approximately 460 ft. with minor variations between individual ships.[9] An important enhancement was specified for the MACs' machinery. A standard diesel tramp engine developed 2500 BHP to give a service speed of 11 kts but to provide some margin for flying operations, all the new-build MACs were fitted with engines rated at 3300 BHP which, in the grain ships, produced a speed of about 12 kts. The new-build tankers with their higher displacements were still capable of 11 kts. while the pre-existing 'Triple Twelves' had a service speed of about 10.5 kts.[9]

The merchant aircraft carriers were modified bulk grain carriers or tankers built with flight decks and small island structures. Minimal aircraft handling and accommodation facilities were available. The bulk nature of the cargoes did not need deck mounted cargo-handling gear used for general cargoes. The MAC-ships were manned by a Merchant Navy crew, under merchant colours, the Royal Navy provided the air department and the guns were manned by DEMS soldiers. They carried their regular cargo in addition to operating aircraft. Tanker MAC-ships were able to carry about 80 percent of their original cargo, the remaining space being taken for Avgas stowage to Admiralty safety standards. Grain carrier MAC-ships suffered a reduction of about 3,000 tons (or 30 per cent) of the original cargo of grain. Their Fairey Swordfish aircraft carried out anti-submarine patrols around the convoy.[34][35]

The scale of the conversion was small, hence it could be completed in a short time; five months has been quoted as being typical.[1]

The fuel piping arrangements in a tanker made it impossible to build a hangar under the flight deck, so tanker conversions were limited to embarking three Fairey Swordfish which had to be kept on deck. Collapsible deck-edge wind breaks were fitted on the flight deck aft to provide some protection for parked aircraft. The grain carriers had a small hangar aft with a single lift which allowed the carriage of four Swordfish. Flight decks were around 460 feet (140 m) long on the tankers and between 413 ft (126 m) and 424 ft (129 m) for the grain ships, width was 62 feet (19 m) in all cases. All the MAC-ships were fitted with four arrester wires. The permanent deck park of the tanker MAC-ships required a barrier for aircraft recovery. Aircrew accommodation was minimal and ammunition and fuel stores were neither armoured nor partitioned.[35]

Many of the ships were given names with the prefix "Mac-", in a reference to their designation as MACs; the "Empire" prefix was used on ships built by the Ministry of War Transport to distinguish them from pre-war privately owned ships. Since these ships were owned by the Government and only on loan to the shipping companies it was easier to take them out of service for conversion.

Air party

Members of the air party and two Fairey Swordfish on the snow-covered flight deck of the MV Ancylus.

The 'air party' was the Fleet Air Arm personnel who flew and supported the aircraft. It consisted of an air staff officer (lieutenant commander), the aircrew, a doctor, a batsman (landing control officer), ten ship's gunners, four signalmen, and three or four able seamen. Under Board of Trade regulations and to comply with the Geneva Convention they were signed onto the ship's articles as merchant ship officers and ratings. Officially they were entitled to the nominal sum of 1 shilling per month on articles, but in practice this was rarely if ever paid. The Merchant Navy part of the crew might have an extra mate and/or wireless operator but was otherwise unchanged.

The aircrew on each ship formed one flight of the MAC-ship wing which consisted of 836 and 860 Naval Air Squadrons, based at HMS Shrike, RNAS Maydown, near Derry in Northern Ireland. 836 NAS was manned by the Royal Navy and 860 NAS was manned by Dutch personnel and assigned to the two Dutch MAC-ships.

An informal, illegal benefit for aircrews was their ability to smuggle contraband without paying import duties. Aircraft were flown off to RNAS Maydown laden with goods which were usually unloaded and hidden before HM Customs could intervene.[1]

Aircraft

Fairey Swordfish at an airshow in 1988. This aircraft was assigned to 'L' Flight of 836 Squadron on board the MAC ship Rapana during World War II

Two aircraft types were considered for use on MAC ships: the Swordfish and the Vought SB2U Vindicator (known in British service as the "Chesapeake"). Fifty Chesapeakes were delivered, but after a three-month trial, they were deemed unsuitable by the Admiralty and relegated to a training role.

In practice, the MAC ships were successful. The apparently antiquated, but robust, Swordfish aircraft were suited to the conditions and their patrols were very effective. They flew more than 4,000 sorties in all. Wartime records show that no convoy with an accompanying MAC ship ever lost a vessel to U-boats, nor was any MAC ship lost.[1]

Ships

New-build grain carriers

Approximately 8,000 tons deep load, 12 knots, 4 aircraft, crew 107, launched December 1942-January 1944. Equipped with hangar and lift. Armament: 1 x single 4 in (102 mm) QF MK IV, 2 x single 40 mm Bofors, 4 x single 20 mm Oerlikon cannons.[34][35]

New-build oil tankers

Approximately 9,000 tons deep load, 11 knots, 3 aircraft, crew 122, launched May–July 1943. BP tankers. No hangar and lift; aircraft maintained and stored on deck. Armament: 1 x single 4 in (102 mm) QF MK IV, 8 x single 20 mm Oerlikon cannons.[34][35]

'Triple Twelve' oil tankers

8,000 tons standard, 16,000 tons deep load, 12 knots, 3 aircraft, crew 118 (64 RN plus 54 MN), converted 1942-44. Anglo-Saxon Petroleum Company tankers. No hangar and lift; aircraft maintained and stored on deck. Armament: 1 x single 4 in (102 mm) QF MK IV, 2 x single 40 mm Bofors, 6 x single 20 mm Oerlikon cannons.[34][35]

Amastra and Ancylus ceased operating Swordfish in late 1944, the empty decks often being used to ferry aircraft from the USA to the UK.[35]

See also

References

  1. ^ a b c d e f Wragg, David (2005). The Escort Carrier in World War II: Combustible, Vulnerable, Expendable!. Barnsley, UK: Pen & Sword Maritime. pp. 12–24. ISBN 1-84415-220-0. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  2. ^ The National Archives: Public Record Office (TNA:PRO), ADM 1/17628, Voyage Report - mv Alexia
  3. ^ TNA:PRO, ADM 1/14950, First Lord of the Admiralty to Mr G Klass dated 30 July1943
  4. ^ TNA:PRO, ADM 234/383, The Development of British Naval Aviation, Volume I, p. 152.
  5. ^ a b c d Friedman, Norman (1988). British Carrier Aviation: The Evolution of the Ships and their Aircraft. London, UK: Conway Maritime Press. pp. 179–181. ISBN 0-85177-488-1. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  6. ^ Roskill, Captain S.W. (1954). The War at Sea 1939-1945, Volume I. London, UK: HMSO. p. 477. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  7. ^ TNA:PRO, ADM 234/384, The Development of British Naval Aviation, Volume II, p. 110.
  8. ^ Schofield, B. B., 'The Defeat of the U-Boats During World War II' in Journal of Contemporary History Vol. 16, No. 1 (January 1981), p. 125.
  9. ^ a b c d e Lenaghan, J (1983). Selected Papers on British Warship Design in World War II. London, UK: Conway Maritime Press. pp. 43–62. ISBN 0-85177-284-6. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ Poolman, Kenneth (1972). Escort Carrier 1941-1945: An Account of British Escort carriers in Trade Protection. London, UK: Ian Allan. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  11. ^ National Maritime Museum (NMM), Ship's Cover 667Y, Escort Carriers Converted from Grain Ships etc.
  12. ^ TNA:PRO, MT 59/1966, Minute dated 29 June 1942
  13. ^ TNA:PRO, MT 59/1966, Admiralty to Ministry of War Transport dated 1 September 1942.
  14. ^ NMM, Ship's Cover 667Y, Controller to ACNS(T) dated 1 October 1942.
  15. ^ TNA:PRO, MT 59/1966, Minute dated 29 June 1942
  16. ^ TNA:PRO, FO 371/32584, Construction of Merchant Aircraft Carriers: Joint Memorandum by First Lord of the Admiralty and Minister of War Transport dated 27 October 1942.
  17. ^ TNA:PRO, CAB 65/28.17, War Cabinet Conclusions 147(42) of 29 October 1942.
  18. ^ TNA:PRO, MT 59/1966, BADW to Admiralty dated 27 November 1942.
  19. ^ NMM, Ship's Cover 667Y, DMB to DNC dated 9 June 1942.
  20. ^ TNA:PRO, MT 59/1966, Minute dated 12 November 1942.
  21. ^ TNA:PRO, MT 59/1966, Anglo-Saxon to Ministry of War Transport dated 2 February 1943.
  22. ^ Howarth, Stephen (1992). Sea Shell: The Story of Shell's British Tanker Fleets 1892-1992. London, UK: Thomas Reed Publications Limited. pp. 114–119. ISBN 0-947637-32-X. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
  23. ^ TNA:PRO, MT 59/1494, Minute dated 19 January 1943.
  24. ^ TNA:PRO, MT 59/1494, Edelsten to Hurcomb dated 11 February 1943.
  25. ^ TNA:PRO, MT 59/1494, Minute dated 17 February 1943.
  26. ^ TNA:PRO, MT 59/1494, Hurcomb to Moore dated 11 May 1943.
  27. ^ TNA:PRO, FO 371/32584, Waldock to Steel dated 27 December 1942.
  28. ^ TNA:PRO, ADM 1/14179, Draft Acquaint and minutes dated 3-18 March 1943.
  29. ^ TNA:PRO, FO 371/32584, Construction of Merchant Ship Aircraft Carriers, Steel to Dean dated 29 October 1942.
  30. ^ TNA:PRO, FO 371/32584, Joint Memorandum dated 27 October 1942.
  31. ^ TNA:PRO, FO 371/32584, Le Rougetel to Waldock dated 12 January 1943.
  32. ^ TNA:PRO, ADM 1/16111, Minute by DTD dated 18 September 1944.
  33. ^ TNA:PRO, ADM 1/16111, Admiralty to the Masters mv Acavus, Amastra, Ancylus, Rapana dated 25 September 1944.
  34. ^ a b c d Mitchell, W H, and Sawyer, L A (1990). The Empire Ships. London, New York, Hamburg, Hong Kong: Lloyd's of London Press Ltd. ISBN 1-85044-275-4. {{cite book}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
  35. ^ a b c d e f Hobbs, David (1996). Aircraft Carriers of the Royal and Commonwealth Navies: The Complete Illustrated Encyclopedia from World War I to the Present. London: Greenhill Books. pp. 231–248. ISBN 1-85367-252-1. {{cite book}}: Cite has empty unknown parameter: |month= (help)
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