The engineer, Delmar G. Roos, is the key person in this article. If you want to look him up on the internet, then add 'Barney' to his name, because under this name he is more well known in the motor vehicle sector. He had everything that a man could wish for, good looks, was a highly praised engineer and had a number of other talents as well, e.g., as a photographer.
He studied mechanical- as well as electrical engineering and gathered a great deal of experience at, among other companies, Locomobile, Studebaker, Pierce-Arrow and even at the Rootes Group in Great Britain, before he came into Willys (Overland) as chief constructor. He joined the company in 1937, just in time to redesign a four-cylinder engine, which later became the 'Go Devil' engine.
The reason why this is so significant, after all, he had already got considerably larger engines going, was that this Willys engine was to take part in a competition to decide who would be the first company in history to deliver a lightweight all-wheel drive (later called the Jeep), in this case, for the US-army. You've probably guessed, Willys did win, although the Bantam Car Company did in fact, produce more and also more punctual development work.
It was this engine, although Roos did not design it, he did reconstruct it, improving it's essential functions. It was called the 'Go Devil', and because of its overlong-stroke it produced a very high torque. Among other things, Roos conjured up counterweights on the crankshaft. Listen to its smooth running in the first video.
This was by far not everything. He improved the durability on the whole, e.g., by changing and/or replacing bearings and valve springs with larger ones. The servicing needs were also considerably reduced. It was as if he had anticipated the forthcoming invitation to bid, since these were all aspects which made it suitable for application in the world war.
Willys could have given the engine to the Bantam Car Company, since their vehicle was much more lightweight. Indeed, they wanted to win. They had to win, because Willys, like Bantam, were directly facing insolvency. Once again, Roos played his trump-card, he slimmed down the draft so cleverly, that he won the favour of the army's jury. The result was: Jeep is still around today, even if it has passed through any number of very differing hands before finally landing at Chrysler-Fiat.
Perhaps the fate of this engine will interest you. Despite mostly having an annual model-change, the basic construction, from the 1930s, could be held onto for a long time. Although it did occasionally disappear for a while and there was even an OHV-four-cylinder, the Go Devil engine with the F-cylinder head was, indeed for the last time, the standard engine in 1970 (!), there was however, at the same time, also the option of having a six-cylinder instead. 11/14