More to what PN was saying, I think MR1 sensors were operated according to different sqn / crew procedures, perhaps varying over time also. My crew, on 201 late 70's, didn't have a loadie although the odd one was still about (remember "Loadie" Brown on 42)? Only the dry team did radio, although we dabbled with "one nominated wetman". He wasn't very good though, and didn't like sitting there. Third sonics was done by one of the junior dry team (i.e. me), thus allowing the Lead wet to monitor sonics / jez / tac nav. As soon as I went "hot" on Sonics 3, the buoy would be taken off me, given to one of the wettys on their (decent) sonics receivers, and I would be given another cold one to monitor. Not a pleasant experience in D807 on a windy night, with two pipe-smoking old crustys sat on either side of me.......
I should make it clear Third Sonics was an add on to the original fit. It was a simple audio receiver, placed between the two Mk1c Sonics displays. All I had to do was listen to the active buoy "ping", and if I heard a return, tell the Lead wet behind me. I also had a sonics stopwatch to roughly measure the range.
When we converted to the MR2, the dry team went up to four (I think based in part on the earlier success of the Loadies), making a crew of 13.