Navy vessel is a term used to describe any type of ship that is used by the navy. A troopship (9 letters) is a type of navy vessel that is used to transport troops and their equipment. A SUB (3 letters) is a submarine, which is a type of underwater vessel used by the navy for reconnaissance and combat operations. Lastly, a flagship (8 letters) is the lead ship in a fleet of vessels, usually commanded by the highest ranking naval officer.