When moving whole units, shipping is always the cheaper, higher-capacity option. Slow speed and port access are the big issues, but what if ship transit times could be cut sharply, and full-service ports weren’t necessary? After Australia led the way by using what amounted to fast car ferries for military operations, the US Army and Navy decided to give it a go. Both services leased Incat TSV/HSV wave-piercing catamaran ship designs, while the Marines’ charged ahead with very successful use of Austal’s Westpac Express high-speed catamaran. These Australian-designed ships all give commanders the ability to roll on a company with full gear and equipment (or roll on a full infantry battalion if used only as a troop transport), haul it intra-theater distances at 38 knots, then move their shallow draft safely into austere ports to roll them off.
Their successful use, and continued success on operations, attracted favorable comment and notice from all services. So favorable that the experiments have led to a $3+ billion program called the Joint High Speed Vessel. These designs may even have uses beyond simple ferrying and transport.