I'm in the Navy.  Have you ever been in the military? 
No I haven't but I know that the navy or maritime force is waterborne military watercrafts.
What are your favorite ships in the Navy? 
There are so many to choose from like submarines, surface ships, amphibious ships, and seaborne aviaton.
Pick one that you like the most.
Submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. It is also sometimes used historically or colloquially to refer to remotely operated vehicles and robots, as well as medium-sized or smaller vessels, such as the midget submarine and the wet sub. 
Although experimental submarines had been built before, submarine design took off during the 19th century, and they were adopted by several navies. Submarines were first widely used during World
Navy
A navy or maritime force is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake-borne, riverine, littoral, or ocean-borne combat operations and related functions. It includes anything conducted by surface ships, amphibious ships, submarines, and seaborne aviation, as well as ancillary support, communications, training, and other fields. The strategic offensive role of a navy is projection of force into areas beyond a country's shores (for example, to protect sea