What kinds of messages would submarines send during a patrol?

Submarines did not often transmit messages because doing so gave away their presence and could give away their exact location. However, there was still the need to get the most important messages out.

The most important messages were those regarding enemy convoys or warships that got past the submarine. This might allow other boats in the area to find the targets and attack. The message would have been brief but would need to include the number and types of ships, last known base course (without zigs and zags) and estimated effective speed.

Other messages could include results of attacks. These would normally have been sent when the boat was clear of the attack area or in relatively safe waters. Boats would also report when they were headed back to port because they were out of torpedoes, short of fuel or had serious damage and needed to end the patrol.

Submarines would also communicate with each other. This would normally have been done using high frequency radios with limited range so that it would be less likely to have been intercepted. Once our boats started operating in small wolfpacks in the fall of 1943, communications among them became very important. Boats had to coordinate operations to be more effective. To assist with this, a radar was added to one of the periscopes with a Morse Code (telegraph) key. The radar transmission would be very directional, thus reducing the chances of it being intercepted. Another option would have been to rendezvous and discuss tactics verbally.