Right Arm Rates

These were established in 1841 and disestablished 2 April 1949, originally signified men of the Seaman branch.

During WWII these rates included Boatswains Mate, Turret Captain, Signalman, Gunners Mate, Fire Controlman, Quartermaster, Mineman, and Torpedomans Mate. Other ratings wore rates on the left sleeve.

https://www.thebalance.com/navy-uniform-history-4054148

I believe Sonarman were included.

My recollection was that right arm rate men were seaman who had the capable of handing small boats

A cursory look also reveals all these men served above deck.