Fireman Recruit - The "Fireman" designation refers not specifically to fighting fires, but is a designation that one gets when in the engineering groups (engines, boilers, electrical, etc.) and, of course, does include firefighting duties. That used to be known as "Damage Control Technicians," but I believe it's now called "Hull Technicians."
Advancement would be to "FA - Fireman Apprentice" and then to "FN - Fireman" before going to a designated rate as Petty Officer 3rd Class.
The same progression for the "deck" ratings (Boatswains Mate, clerical, actually most of the standard jobs) would be "SR
- Seaman Recruit" and the SA and SN accordingly.
In the air groups you would have "AR - Airman Recruit" and then AA and AN, and so on.