 His release, which was delayed until March 1642 because the imperial government feared to see Horn at the head of the Swedish army and would not allow an exchange.When at last Werth reappeared in the field it was as general of cavalry in the imperial and Bavarian and Cologne services.His first campaign against the French marshal Guebriant was uneventful, but his second (1643) in which Baron Franz von Mercy was his commander-in-chief, ended with the battle of Tuttlingen in which Werth was instrumental in a surprise victory.