Submarines and aircraft carriers were of little use against irregulars relying on sampans and junks to ferry supplies and fighting men on the Vietnam's river highways.
Mallows Bay is known for its "Ghost Fleet," including partly submerged remains of more than 100 wooden steamships that were built in response to threats from World War I-era German U-boats.
The Coast Guard says unlicensed vessel operators need to be aware that taking members of the public out for hire is illegal and not a legitimate way of supplementing income.