Zentner

Lieutenant Rudolph Zentner was a German naval officer on the U-20 under Captain Walther Schwieger.

In an alternate timeline, Zentner rescued the Fifth Doctor and Helen after the U-boat had sunk the ship they were on, thus starting a chain of events which led to the RMS Lusitania not being sunk. (AUDIO: The Sirens of Time)

Behind the scenes

 * Historically, Zentner was not on board the U-20 when she sank the Lusitania.