He earned a reputation as an overly aggressive commander, which caused him to be placed on a black-list of officers the Allied powers considered to have breached the laws of war.

He next took command of the Widder and sailed her into the Atlantic Ocean on 6 May 1940, commencing a five-month cruise that would sink or capture ten enemy merchant ships.

When he brought Widder into port at Brest, he refused the Naval Command's order to take the ship to Hamburg, because the passage through British controlled territory was too risky.

Zippel tried to define the limitations of international law, called Vizeadmiral Bernhard Rogge as an expert witness, and questioned the testimony of the British sailors.

In closing, he asserted that "the law has recognized that in matters of sea even clever people are more liable to commit an error than in other walks of life".

[1] Ruckteschell died in the Hamburg-Fuhlsbüttel prison on 24 June 1948, shortly after he had been informed that he was going to be released due to his deteriorating heart condition.