The SpaceX recovery ship Go Quest heads into Port Canaveral while in front of it is the U.S. Navy’s Expeditionary Fast Transport vessel named City of Bismarck. The Go Quest supports ocean landings of SpaceX Falcon 9 rockets on the autonomous spaceport drone ship, sort of a rocket landing pad on a barge, that is then towed back to Port Canaveral so the rocket can be refurbished and reused. In this case, the return of the booster on 12 September 2018 used for the launch of Telstar 18 Vantage. The City of Bismarck, on the other hand, is a little more complicated. From the U.S. Navy Fact File:
The Expeditionary Fast Transport (EPF), formerly designated the Joint High Speed Vessel (JHSV), is a shallow draft, all aluminum, commercial-based catamaran capable of intra theater personnel and cargo lift, providing combatant commanders high-speed sealift mobility with inherent cargo handling capability and agility to achieve positional advantage over operational distances. Bridging the gap between low-speed sealift and high-speed airlift, EPFs transport personnel, equipment and supplies over operational distances with access to littoral offload points including austere, minor and degraded ports in support of the Global War on Terrorism (GWOT)/Theater Security Cooperation Program (TSCP), Intra-theater Operational/Littoral Maneuver and Sustainment and Seabasing. EPFs enable the rapid projection, agile maneuver and sustainment of modular, tailored forces in response to a wide range of military and civilian contingencies such as Non-Combatant Evacuation Operations (NEO), Humanitarian Assistance and Disaster Relief (HADR).