GE Hybrid Tank (1918-12-24) by General Electric CompanyMuseum of Innovation & Science
While some military planners thought that tanks were useless gimmicks, some recognised that they were the future of warfare. The US army needed a tank, fast. Thankfully, they had a thriving car and agricultural industry, and inventive engineers…
The very first American tank was built by a partnership of the Holt Manufacturing Company (now Caterpillar Inc.) and the General Electric Company. Their design was radical; an existing Holt model 75 tractor fitted for speed and reliability with a hybrid gas-electric engine.
GE Hybrid Tank Drawing (1917-05-25) by General Electric CompanyMuseum of Innovation & Science
This scale drawing shows the design in three dimensions. There would be a crew of six (commander, driver, two machine gunners, a main gunner and a loader) protected by boxy 15mm steel armour, carried on caterpillar tracks driven by the hybrid engine.
Unlike modern plug-in hybrid vehicles, the gas and and electric engines weren't separate. The gas engine powered electric generators, which in turn powered electric motors attached to the tracks. The result was… unwieldy and unreliable, but not unprecedented…
The French Saint-Chamond tank was based on a hybrid engine installed on Holt tracks. But Holt's implementation was particularly prone to overheating, so a complex water-cooled radiator system was installed, and the crew always had the option of opening the rear door.
GE Hybrid Tank, 1918 (1918-12-24) by General Electric CompanyMuseum of Innovation & Science
The prototype was put through its paces in 1918 and was unsatisfactory in almost every way. The radiator increased the weight of the tank to 25 tons, the 90hp engine struggled, the tank's top speed was a snail's pace 6mph on the flat… and nothing on an incline.
GE Hybrid Gun Mount (1919-12-30) by General Electric CompanyMuseum of Innovation & Science
The tank was an utter failure, and quickly scrapped. Instead a variation was tested as a gun mount and tractor. In this role it was more successful, but by this time the armistice had been signed and the war was over.
Renault tank during WWI (20th Century)National WWI Museum and Memorial
LIFE Photo Collection
That said, the US military hasn't looked away from pioneering propulsion technologies. The M1 Abrams, its main battle tank, was the first to use a turbine engine, producing a respectable 1500hp. And plans currently exist to use hybrid engines in future armoured vehicles.