Being a "Captain" on a commercial vessel isn't just a title, it HAS to be backed up by multiple certifications and licenses issued by the USCG based on demonstrated competency via "real world" testing for the size and horsepower of the vessel. In the case of the LST, the "Captain" was a freshly-minted cap for that size/horsepower....up-graded from a small-craft charter boat license. Not exactly a major "confidence-builder"! It worked, he got the vessel back to the US without significant incident....but I can understand why even the bureaucrats were somewhat nervous....driving a 350' twin-screw steel ship isn't quite the same as pushing a 28' Bayliner!
Unless the vessel captain is also a licensed pilot for the specific waters the vessel is entering, then a Licensed Pilot is required by law.