Why frogmen are chiefly a carrier threat in port

Could frogmen attack a carrier despite fleet defences centred on missiles and submarines?

Most plausibly in port, where layered harbour security should detect and stop them before they reach the ship.

Italian-style frogmen or similar raiders would threaten a carrier chiefly while it was in port, where harbour protection is meant to stop them. A successful attack in a United States home port would expose failures by the agencies responsible for coastal and port security as well as by the navy. Protection of a deployed task group differs from the surveillance, policing, and access-control problem around a naval base. The answer therefore places the main defensive burden on layered harbour security.