In early 1800, Klenau transferred to the K(aiserlich) und K(oeniglich) (Imperial and Royal) army of Germany, in Swabia, under the command of Feldzeugmeister Paul, Baron von Kray. The 1800 campaign in southwest Germany began on 1 May 1800, at the village of Büsingen, east of Schaffhausen (Switzerland); there a small force of 6,000 men under command of General of Brigade François Goullus defeated 4,000 men, three battalions of the 7th Infantry Regiment Schröder, commanded by Lieutenant Field Marshal Karl Eugen, Prince von Lothringen-Lambesc. Following this clash, the impenetrable Württemberg fortress, Hohentwiel, capitulated to the French, in what the Duke of Württemberg considered a scandalous lack of military courage.