Scary....I don't see an easy way to protect military or civilian floating assets right off the top of my head other than to try to break our enemies will to fight..do you?
My experience with merchant ships at night is that they are dark unwieldy leviathans quite vulnerable to anyone with the cajones and the knowledge.
Heck, sinking a ship in the shipping channel or sinking several ships pierside would promote economic terror.
Salvage operations would be expensive, you'd loose use of the port/pier, spread fear, etc. Yep, low cost, high impact. Coming to a port near us soon?
As long as we have enemies on our soil who want to commit acts of terrorism and sabotage against us, there is NOTHING we can do to stop them.
There are just too many targets to protect. Ships are just one category of big easy targets.