The list of units
While barely able to defend itself, the Transport can move large quantities of military forces over the bounding main. A transport carrying Marines can be a significant off-shore threat to any nation.
A coastal city needs oil in its Strategic Resource box to build a transport.
The troop transport ship, which in peacetime serves as a cargo or passenger vessel, is the principle means used by modern powers to move large quantities of military equipment and personnel over long distances. Because transports lack offensive weaponry, they require armed vessels as escorts during times of war. A properly escorted transport can move large military forces to a new area quickly to act as reinforcements or as an attacking force.