A number of Austrian accounts of the 1800 campaign mention a Oberst (Colonel) Williams who helped to organise a naval flotilla on the Bodensee (Lake Constance) to fight the French. The list of Officers of the British Army and the Corps of Royal Marines for 1798 mentions a Lieutenant-colonel Richard Williams of the Royal Marines, could this be the officer in question?
Any help would be greatly appreciated.
After some more research not a British officer at all:
James Ernest Freiherr von Williams, born around 1762 †August 27, 1804 Vienna. Commissioned by Emperor Joseph II in Ostend in
Imperial service, 1789 Major, commander of the Corvette Maria Theresa operating on the Danube.
1795 commander of the Rhine flotilla. 1796 lieutenant colonel, 1797 commander of the Corvette L’Austria, 1803 Colonel and retired. 1795 RK of the MMThO
."Austria raised two naval establishments: the "Trieste Navy" consisting of the two early gunboats and commanded by Col. James Ernest von Williams, and the "Venice Navy" commanded by Venetian aristocrat Andrea Querini holding authority only over the Arsenal."
http://www.centotredicesimo.org/wp-content/uploads/2015/10/ACERBI-The-Austrian-Imperial-Army-1805-09.pdf