The Duesenberg brothers built every type of engine for road and track, air and sea, but the biggest of them all was a WWI aircraft engine of 3,393 CID and up to 900 hp.

Fred and August Duesenberg are celebrated today for their three Indianapolis 500 victories in 1924, 1925, and 1927, and for the mighty Model J road car introduced in 1928. But years before that, they were already recognized as master engine builders for racing, marine, and aviation use. So when the USA entered World War I in 1917, the Duesenbergs’ financial backers set up a state-of-the-art manufacturing plant in Elizabeth, New Jersey, where the Duesenberg Motors Corporation was awarded a contract to build 2,000 Liberty aircraft engines.

The order was soon changed to an equal number of Bugatti-King U16 engines, giant 410 hp beasts with twin crankshafts and 1,484 cubic inches. But the project was slow in developing (only around 40 were built) and meanwhile, Fred Duesenberg had ideas of his own for an even larger and more powerful aircraft engine, one capable of an astounding 800 hp. The U.S. military ordered four engines for testing and evaluation.

Duesenberg and his engineering staff, which then included C.W. Van Ranst, laid out a 45-degree V16 with a bore and stroke of 6.00 inches by 7.50 inches, for a total of 3,393 cubic inches. The 16 cylinder jugs were each built up from a machined cylinder barrel and a set of eight 18-gauge steel stampings, gas-welded together to form a water-jacketed assembly in the Mercedes style.

There were three valves per cylinder, one intake and two exhausts, all operated via Duesenberg’s signature walking beam mechanism (above). The walking beam, a feature of many early Duesenberg engines, was essentially a long rocker arm that transmitted motion from the camshaft in the block to the valves in the cylinder head, with the valves arranged horizontally in a compact vertical combustion chamber. Four Miller updraft carburetors provided the fuel, and twin ignition with two Delco battery-powered distributors and a pair of Dixie magnetos provided the spark.

The Duesenberg H, as the monster was designated, was expected  to produce 700 hp in direct-drive form and 800 hp with a .758:1 gear reduction unit that allowed greater crankshaft rpm. Early tests, conducted on a special rig (above) that consisted of three Sprague electric dynamometers lashed together, were promising and it appeared that 900 hp was within sight. But there were the usual teething problems as well, and while the first official military test for the engine was scheduled for Dec. 31, 1918, the Armistice was signed on November 11 and the war was over.

At more than seven feet long, the Duesenberg H was too large for any winged aircraft then in use by the USA. In the photo below from the New York Aero Show, the V16 dwarfs even the King-Bugatti U16, which was two 12-liter straight eights on a common crankcase, more or less. In displacement, it was the largest Duesenberg engine ever (though the brothers’ 1914 inline-12 marine engine came rather close at 3,221 CID).  Two of the mighty H engines still exist: one in the collection of the Smithsonian’s National Air and Space Museum, and the one shown here, which you can see at the Auburn Cord Duesenberg Museum in Auburn, Indiana.