Operations Specialist.
In the US Navy, OS stands for Operations Specialist. Operations Specialists are responsible for maintaining situational awareness and providing tactical support during naval operations. They operate radar and communication equipment, track and analyze targets, and provide critical information to commanding officers.
Possibly a Flight Engineer
I haven't heard that term when relating to the US Navy. But in the Royal Navy SDG is a scubadiver
Yes. The Enlisted rate for medical personnel in the Navy is Hospital Corpsman (HM)
MOS would be most interchangeable with Rate in the navy. Rate is pretty much another word for job specialty as is mos. Rate may also be referred to as a NEC.
United States.
This is called a "rating" in the Navy. The AT denotes that person's rate, or job. In this case, it is an Aviation Technician. The 3 denotes that person's rank, which in this case, is a 3rd Class Petty Officer.
The enlisted rate who sits at the radar console on watch is typically an OS (Operations Specialist). The guys who actually do technical work/repairs/maintenance, depending on the type of radar, are usually FC's (Fire Controlman) or ET's (Electronic Technicians). Radarman or Radar Operator is no longer a rate in the US Navy.
1949
"Rate" refers to a non commissioned member of the US Navy.
Not SSK3c, but SK3c is the old rate designation for Ship's Storekeeper, 3rd Class. The Storekeeper rate, one of the oldest in the Navy, has always used the designator SK. Today the rate/rank would be designated SK3.
SEa Air and Land
submersible boat