Two types of gunners for US. Reload (REL) and Accuracy(ACC)  You can choose at each stage which to focus on.  So for your first step above armament sailor you could choose accuracy(ACC) then at the next step choose reload(REL) and then accuracy for the 3rd step.  that is what is meant by ACC/REL/ACC 

Whatever you choose, either accuracy or reload gets the biggest ability boost for that stage.   Hope this helps.

The stats of your gunner can change your choices but perhaps RLD/ACC/RLD might be better than A/R/A but it's been a while since I've done USN

Acc-acc-rld or rld-acc-rld are probobly the better choices.

You choose the promtions, at levels 22, 42, and 65.

-Moved to the US Navy section

R/A/R Thanks for the big help guys, now i get it. GodSpeed!!