German commander speaks via radio and he does that three times, as I remember. Probably it's taken from the book? I never read it.
It should be technically possible, I guess. But the implementation is really "hollywood", evil Nazi who acts as ... really evil Nazi.
Real story:
Soviet merchant ships carried special UHF equipment called Akatsia which was to be used strictly for communication with the Soviet Navy and Air Force. The box was super-secret, the radio officer needed special approval for any maintenance/repair and quartz crystals were changed on a regular basis. It was closed in a special case and sealed when the vessel was in the territorial waters of other countries. One day (in 1988, I guess) our ship sailed right into the area of US-South Korean drills. Once we approached the perimeter of a carrier group we were called on international UHF channel (via normal "civilian" radio) by US destroyer. Since we were slow to respond, they called us again... this time on the super-secret frequency of Akatsia. That was very convincing.