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U3  VETERANS CREW   

Radio operator

The radio operator could send diving reports, safety messages and intelligence reports when the HF antenna could be hoisted above the surface.
When submerged he could only receive very low frequency signals VLF down to 30 m depth. In such cases the submarine was only receiving signals and the radio operator couldn't acknowledges the signal.
Most of the traffic was encrypted telegraphy in the high frequency band, 3-30 MHz, utilising two HF receivers and a 50 W
HF transmitter. The boat also had a radio station operating in the VHF band to be used as short distance telephone when on surface.

You can here listen to typical encrypted radio message! Here follows an explanation on the sample.

Two radio operators served, ships number 53 and 54, and they had to work on a two watch system.
Besides the duty in radio communications they handled the mail and some office duty. It was a welcome task to go ashore to see the post office.

Submarine U3 Direction finding receiver, HF antenna tuning box, antenna switch and the VLF receiver.
U3 Direction finding receiver, HF antenna tuning box, antenna switch and the VLF receiver. Photo U3 archives.

Submarine U3 Two HF receivers and the telegraph key. Submarine U3 HF transmitter.
U3 Two HF receivers and the telegraph key. Right the HF transmitter. Photo U3 archives

Submarine U3 Tuning the HF receiver.
Tuning the HF receiver. Photo U3 archives.