Wikipedia
Sealift is a term used predominantly in military logistics and refers to the use of cargo ships for the deployment of military assets, such as weaponry, vehicles, military personnel, and supplies. It complements other means of transport, such as strategic airlifters, in order to enhance a state's ability to project power.
Sealift shipping falls into three broad categories: dry cargo freighters, liquid tankers, and passenger or troop ships. During joint operations, dry cargo ships may transport equipment and supplies required to conduct and sustain the operation; tankers carry fuel; while passenger and troop ships carry personnel to the theater and allow the evacuation of noncombatants or those in need of medical aid.
Sealift can also be divided into strategic and tactical sealift. Strategic sealift is the transportation of vehicles and equipment to a staging area equipped with port facilities, with personnel arriving by other methods. Tactical sealift occurs when a ship is carrying personnel along with vehicles and equipment, and is able to deploy them directly and operationally, like in an amphibious assault.
While ships are slower than their airborne counterparts and may require port facilities to unload their cargo, their larger capacity allows them to transport heavy armoured forces or bulky supplies that only the largest strategic airlifters (such as the C-5 Galaxy) could normally handle, and in much greater quantities.
A state's sealift capabilities may include civilian-operated ships that normally operate by contract, but which can be chartered or commandeered during times of military necessity to supplement government-owned naval fleets. Some smaller navies have built multi-role vessels that combine sealift with other capabilities, such as those of a patrol frigate or a command-and-control vessel. The Royal Danish Navy's and the Royal New Zealand Navy's multi-role vessel being two examples.