In the U.S. Navy, 112X is an Unrestricted Line (URL) Officer who is qualified in Submarine Warfare.
Other URL Officer designators include:
111X, qualified as a Surface Warfare Officer
113X, qualified as a Special Warfare Officer (SEAL)
The U.S. Navy’s submarine force is the most capable in the world. It includes:
53 fast attack submarines
14 ballistic-missile submarines
4 guided-missile submarines
When not engaged in combat, attack submarines patrol the open ocean or a “forward area”.
These areas commonly include:
The Persian Gulf
The Mediterranean
The Western Pacific
The Soviet Arctic
The Sea of Okhotsk