One might regard it as something of an open secret. He originally served in Prussia, under King Frederick the Great, who was also gay (though Von Steuben and Frederick were not close - Von Steuben was just a minor officer of the young-and-coming generation, and Frederick was literally the king, and developing into an old curmudgeon who hated The Kids by the time). After some downsizing in the Prussian military, Von Steuben spent some time as, effectively, an officer-for-hire for the German princely states, since his training as a Prussian officer was top-notch and in high demand at a time when rising through the Prussian ranks wasn't really an option.

Washington had specifically requested Congress get him someone with some legitimate professional experience - as Washington was a good leader, but had only ever led militia, and needed troops who were drilled and trained professionally. So Von Steuben was helped by Ben Franklin to get tf out of Europe on part due to him having sodomy charges in one of the German states he served in (It's uncertain whether the specific charge was true, but Von Steuben's lifelong homosexuality, at the least, made him an inviting target for such accusations by his enemies). He arrived in the US with his secretary and lover, and found the Continental Army at its lowest point - Valley Forge.

He spent his time there training an elite cadre (trained personally by Von Steuben so that THEY could train the rest of the army) and writing the US Army's first drill manual - he wrote it in French, which he was fluent in, so his American aides could translate it into English. The troops he personally drilled he did so by shouting at them in three languages - German, French, and a small smattering of English - and relying on translators to get his point across. Some of the first English words he learned were profanity, so he could curse at the troops he was training. The men loved him for this - soldiers love a little roughness in their officers. It let them know he wasn't some aristocratic twit who was better with table manners than military life!

This drill manual he wrote - the Blue Book - became and remained very influential on the US Army for decades to come. It wasn't just a copy of European drills, though it certainly took heavily from European military standards - it included some innovative thinking on the importance of NCOs (sergeants and the like), and a simplified parade and marching drill that American troops found more useful (in the rough roads of the Colonies) and intuitive. Von Steuben is said to have noted that he could not train American troops like Europeans - they were not used to blindly following orders, and harsh discipline was not an option with the limited manpower the American Revolution had - but once told why an order was important, they were generally enthusiastic to carry it out.

During his service with the Continental Army, he had, at one point, a dinner party for officers wherein everyone was to show up naked. At some point during his service, he met and became 'very close' with two strapping young American officers, whom he would later formally adopt (a common way for gay men before the modern day to provide definite legal ties, such as for inheritance purposes). For obvious reasons, they are widely suspected to have been his lovers.

While he was indispensable to the war effort, he didn't quite get all of what he wanted from his service - Von Steuben craved an independent command of a campaign to gain everlasting military glory, in the spirit of the day. The problem was that Von Steuben was too good at his job - the Continental Army simply couldn't spare him from training men, as he was the only real officer in the whole damn army who had experience with training troops to make large-scale manuevers. So he spent most of the war teaching new recruits and officers how to maneuver on the battlefield - no small task. Having groups of thousands of men all moving and acting in unison without trampling or getting in each other's way is something that requires a great deal of effort and precision to pull off!

Despite this disappointment, he seemed happy with the newfound country when the Revolution was successful. He founded a veteran's society, was granted a pension by Congress, retired in a rural New York mansion, continued to be a fixture of local high society, wrote in defense of democracy over an oligarchy of the rich in state politics, attended George Washington's inauguration, and died peacefully in his home.