«Suddenly something unexpected happened»
The Hughes H-4 Hercules weighed 115 t, was designed to lift a 65 t payload, was 66.6 m long and had a wingspan of 97.5 m. Not bad for a plane built in 1947, whose vital statistics could even compete with the Antonov AN-225, the largest full-freighter in the world, as well as with the Airbus A380, the biggest serially-produced aircraft ever.
source site On 16 February 1945 Franz Rittmann, the editor-in-chief of the newspaper Transport, as the International Transport Journal ITJ was called then, wrote that «aeroplanes, in contrast with ships, the railways and lorries, are one of the war’s winners.» He believed that this was clear even before the fighting ceased in Europe on 7 May 1945. His assessment was underlined by the fact that technological developments in the Second World War had brought about the jet engine. The 1939–1945 war also gave a massive impetus to airmail and airfreight activities. Towards the end of the war a trend towards full-freighters was even discernible, whilst flying boats represented a potential alternative for long-haul operations.
The world’s largest ever flying boat, which still holds the record for the biggest wingspan of any aircraft in the history of aviation, was developed too late for war action, however. The industrialist Howard R. Hughes was asked by the US government to build a large transport plane in November 1942, «at a time when German submarine warfare reached its most intense level,» as the above-mentioned article stated five years thereafter. But assembly of the Hercules HK-1, as it was initially called, only began in June 1946. In late 1947 Hughes announced that the unit was ready for a test swim. The short 45 km transfer from the hangar to the coast cost no less than USD 55,000. The eight engines developed their full 24,000 hp on the third test run on 2 November in the port of Long Beach CA, bringing the plane to a speed of 160 km/h. «Suddenly something unexpected happened – the aeroplane took off from the water very smoothly, and flew for about 1½ kilometres at a height of about 20 m.» The flight, which was carried out within the ground effect, remained the only flight of the so-called Spruce Goose, for planned serial production of the flying behemoth never took place, in the light of the unit’s rather poor cost / benefit ratio.
Other flying boats which made aviation and air cargo history did enter production, however. This group includes the Martin JRM Mars (a small series of seven units built), whose development was started in 1938 and whose maiden flight took place in 1942.
The Martin JRM Mars plane was earmarked for the transportation of troops as well as freight between the west coast of the USA and Hawaii and other Pacific islands during the war. The Caroline Mars, the last aircraft in the series to be delivered (1948), set a new world record on 8 September 1948, when it carried 30 t of cargo over a total distance of 600 km. That is more than short-haul freighters deployed today, such as the Boeing B727 or 737, can transport. After their time with the US Marine Corps the planes were re-fitted as fire-fighting units. In Canada in autumn 2013 the Hawaii Mars II became the last Martin JRM Mars unit to be retired.