Sure, they could have... could you imagine what could have been had the military and congress not been so skeptical and afraid of air transportation when it came to troops. The U.S. blew its chance back in early '42 when Kaiser and Hughs wanted to build the Hercules... had they gotten fully behind the idea instead of restricting materials used and considering it as a crazy idea. Things would have been very different. It would have been completed well within the time frame of D-Day. With a capacity of 750 fully armed troops instead of the C-47's messily 28, and once we had air superiority it could have easily landed battalions behind enemy lines using Frances larger lakes and bays. Germany wasn't expecting invasion by air, even though they had made great use of large transports themselves. Throughout all of WW2 the U.S. was far superior in ability to manufacture in great numbers. But was drastically outclassed in technology and the willingness to follow-through with ideas that they stooped to using manpower in ways as it it was still the civil war.
Phil
I agree that the HK-1 could have made a major contribution to the war effort, but even with massively increased funding they could not possibly have manufactured enough working aircraft to enter combat by the end of the war, let alone by June of 1944. Even with the accelerated pace of the War Years, it took a lot of time to take an aircraft from concept, to development, to prototype, to flight test, and finally to manufacturing.
For example, the North American P-51 Mustang was produced in a phenomenally short time period for its day: the initial development contract was awarded in May, 1940, but by the time all the bugs had been worked out, manufacturing of the P-51B didn't start until the summer of 1943. The first battle-ready aircraft didn't start arriving in Europe until the winter of 1943-44. That's a 3.5-year timeline, from concept to flying the aircraft over Europe. And that was a relatively simple project, a single-engine fighter.
Multi-engine aircraft were and are a much, much more formidable problem for design and manufacture. Boeing began initial development of the B-29 design in 1938, was awarded a development contract in 1939, produced prototype for wind tunnel and other static testing in 1940, but did not produce the first flying prototype until September, 1942. By the time Boeing had worked all the worst of the bugs out of the Superfortress and it was able to fly its first combat mission, it was June, 1944. That was a 6-1/2 year development time. And the B-29 was not an 8-engined aircraft. The complexities involved in producing a reliable airworthy 8-engine seaplane would have exceeded those of the B-29 by a large margin.
The development contract for the HK-1/Spruce Goose/Hercules was awarded in 1942, and was funded as well as any other military aircraft development contract could expect to be. But even if they had had all the advantages North American had with the P-51, and had been able to somehow complete the development process in 3.5 years, HK-1's couldn't have possibly been pressed into war service until 1945 at the earliest. The R-4360 Wasp Major engine (the engine that was eventually used by Hughes in the test flights of Spruce Goose in 1947) was the only engine produced in WW2 that had the power to get the HK-1 airborne, and it wasn't developed until 1944 and production didn't become viable until after V-J Day.
It's amazing that Howard Hughes was able to fly the only prototype in 1947, only 5 years later. But even this wasn't a true service-ready aircraft, as it was only capable of flying a few hundred feet in ground effect, and it's probable that a fully functional HK-1 wouldn't have been available until 1948 or 1949.
