Radio is different on a submarine, in that most of the time you're on watch, you actually can't radio anyone. :) So radio spends a lot of their time routing message traffic, preparing outgoing messages, and then a bunch of day-to-day maintenance/crypto stuff. (On my boat, IT was run by Fire Control division, not Radio.) If anyone spends time in Radio outside of watch, it's because it's pretty private - only officers and people in the radio division can get into the room. No one ever slept in Radio on a submarine.

And yeah, there were about 5-6 people in the Radio division, IIRC.