The Emperor’s Sword:
American Carrier Conversions
by Mike Bennighof, Ph.D.
September 2021

The U.S. Navy’s War Plan Orange called for an advance across the Pacific Ocean in the teeth of well-prepared Japanese bases including airfields on the small islands over which they had gained control following World War One. At least some of those bases would need to be captured, and other new airfields constructed. Aircraft would then need to be shuttled forward to these new bases.

In the mid-1930’s, the United States had only a handful of aircraft carriers: the converted battle cruisers Lexington and Saratoga, and the unsuccessful purpose-built carrier Ranger. New carriers would soon be commissioned, but even with the new Yorktown class and the smaller Wasp, the number of flight decks would be limited. To augment that strength, the Bureau of Construction & Repair looked to convert suitable merchant hulls into aircraft carriers.

These would be fleet carriers, not the escort carriers that were actually built, in vast numbers during the Second World War. They would be slower than the purpose-built carriers, but would operate in the same manner to increase American front-line carrier strength – one of the quirks of Plan Orange in all of its many iterations is that it did not openly admit that American forces might suffer ship losses during their advance across the Pacific.

Construction & Repair began to look at converting liners into carriers in 1923; the 1924 version of War Plan Orange called for nine such carriers, with flight decks at least 600 feet long and a speed of 25 knots. The U.S. merchant fleet had no ships that met those requirements, and the only ones that even came close were either elderly, coal-burning (which made flight operations difficult and refueling at sea impossible), much too slow, or all three. And all of them had already been allocated to the war plan as troop transports.

Liner SS America, as the troop ship West Point.

The 1929 edition of War Plan Orange actually assigned carrier conversions to shipyards, even though no actual ships for conversion were named. The first was to emerge 180 days after mobilization began, with eight more to follow at 30-day intervals. Construction & Repair noted that the conversions could probably be completed faster, but the needed elevators could not be built any faster. If the Navy ordered these key parts early, that might reveal the intention to convert liners into carriers or even indicate which ships had been selected.

By the early 1930’s, American companies had commissioned new liners, and Construction & Repair duly drafted plans for their conversion into aircraft carriers. In all ten liners met the bureau’s requirements, but the war plan now called for twelve carrier conversions, so the decrepit coal-burning ships Monticello and Mount Vernon joined the list. Four of the others appeared on two lists, one for carrier conversion and one for conversion into armed merchant cruisers. The most suitable were the three California-class liners operated by Panama-Pacific Lines and the two Manhattan-class ships belonging to U.S. Lines.

Things began to change in 1936, when the Roosevelt administration established the U.S. Maritime Commission to oversee a total overhaul of the American merchant marine, emphasizing construction of merchant ships in American yards, flying the American flag and manned by American crews. As its first project, the Commission subsidized construction of the big passenger liner America, a 26,000-ton ship with a length of 723 feet – well-suited for Construction & Repair’s carrier needs. Planning for her conversion into a carrier began as soon as her liner plans were finalized.

In 1939, Navy analysts determined that two very large 25-knot liners under construction in Japan for the Nippon Yusen Kaisha had probably been designed for conversion into aircraft carriers. Like most passenger liners of the time, they were built with government subsidies, but their size, deadweight and machinery arrangement hinted at another purpose. Admiral Emory S. Land, the Maritime Commission chairman (and former chief of Construction & Repair), proposed doing the same thing. As initially proposed, the P-4 type liner would come in three sizes, displacing 14,000 tons (for service to South America), 22,000 tons (for service in the Pacific) and 26,000 tons (for routes to Europe).

Emory Land's proposed P-4-P Trans-Pacific passenger liner.

Hoping to gain military funding for new liners, Land proposed a larger ship, the P-4-P. The hull and power plant would be built to naval specifications rather than following civilian practice, with extensive subdivision and the machinery split into two units, one for each shaft. She would have two funnels, already placed on the starboard side of the hull. She would displace 41,000 tons, with a length of 760 feet. Land sought authorization for five such ships, but the handful of shipyards that could construct such a vessel had their slipways full with Navy orders. Seattle-Tacoma, a yard that previously had only built much smaller ships, made a bid for build two at a much higher price than the Commission was offering ($28 million rather than $20 million; of that $20 million, $ million would come from the government and the remainder from the private shipping company who would operate her) but the Commission declined the offer.

The September 1941 war plan revision still called for ten converted carriers, but noted that the conversions were unlikely to be ordered. Those were in addition to the 83,000-ton French passenger liner Normandie, interned in New York in September 1939 and transferred to the U.S. Navy in December 1941. Some American newspapers proposed turning her into an aircraft carrier or combined carrier/troop transport, but this was never an official project and Secretary of the Navy Frank Knox approved her conversion to the troopship Lafayette. While workmen cleared her civilian fittings, a welding torch set a pile of life vests on fire which in turn ignited the varnished woodwork in her first-class lounge, and that was the end of Normandie and any thought of turning her into a Nimitz-sized aircraft carrier.

Liner SS Normandie under Coast Guard control in New York.

By this point, the concept no longer had a purpose. Aircraft continued to grow in size and capability, and with treaty limitations no longer in effect the U.S. Navy had ordered large numbers of very capable Essex-class carriers with the intention of building still more. The liners were better used as desperately-needed troopships, and all of those tabbed for that purpose saw use moving soldiers around the globe.

Japan converted two large liners into the carrier Hiyo and Junyo, and Italy one into the carrier Aquila. Both projects showed that liner conversions required massive expenditures in time, money and labor. While the Japanese ships had been designed and built for ease of conversion, they still took more work than anticipated and did not result in very good fleet carriers. The Italians ended up gutting the liner hull and replacing everything inside; their ship was not completed before Italy left the war.

The Emperor's Sword, our massive Second World War at Sea expansion set, includes ten American liner conversions: four of the pre-war liners, four P-4-P ships, the SS America and of course SS Normandie. They are not very good aircraft carriers, but they are aircraft carriers, and Normandie/Lafayette is by far the largest ship we’ve ever shown in Second World War at Sea (and makes for one big, fat soft target).

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Mike Bennighof is president of Avalanche Press and holds a doctorate in history from Emory University. A Fulbright Scholar and NASA Journalist in Space finalist, he has published an unknowable number of books, games and articles on historical subjects. He lives in Birmingham, Alabama with his wife, three children and his dog, Leopold.

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