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.
It's a job that doesadministrative support for aircraft maintenance
LVA stands for Lieutenant Vice Admiral in terms of royal navy ranks.
FP1 means Pipe Fitter First Class. The 'FP' is the Rate (Pipe Fitter) and the '1' stands for the Rank (Petty Officer First Class).
HM2 refers to the rank of Hospital Corpsman Second Class in the United States Navy. It is a non-commissioned officer rank and indicates that the individual is a petty officer. Hospital Corpsmen provide medical care and support to navy personnel both on land and at sea.
The HM is the rating for a Hospitalman. Most people call them Corpsman. The senior HM in a command is usually referred to as 'Doc' even though he isn't a doctor. The 1 indicates they are a First Class Petty Officer, which is an E-6.
You can find information about navy ranks on the official website of the Navy, as well as on military-specific websites such as Military.com or GlobalSecurity.org. Books on military history and organization may also provide detailed information about navy ranks.
That would be ranks in the Army or Air Force.
Firecontrol Technician second class. An FT2 is an E5 in rank and is responsible for the guidance systems for all large weapons onboard the ship up to and including missles.
AVCM designates a Master Chief (E-9) Avionics Technician
This stands for the rating of "Stoker" and goes back to the days when ships' boilers were coal-fired and thus "stoked" by stokers. In the Royal Navy they are now known as Marine Engineering Mechanics, further divided into Mechanical and Electrical sub branches. Jack
The SEALs are a part of the US Navy. They use the same ranks as the Navy, enlisted personnel would be petty officers and chief petty officers. The Officer ranks would go from Ensign to Captain.
Those who join the Indian navy after clearing the Indian Engineering Services exam , join the naval armament branch of the Indian Navy but not sure about the ranks awarded to them. Even not sure about the uniform of them.