In 1971 the Texas legislature added new responsibilities to the Port Authority, which acquired an additional vessel, in 1973, the Captain W.L Farnsworth.
The vessels are powered by four diesel engines each producing 1,138 shaft horsepower (849 kW), and have a draft of just 34 inches (0.86 m).
Their sensors can see through fog, or in the dark, and will be useful in the vessel's secondary role - countering chemical disasters or attacks.
They vessels have berths, for sleeping, for extended missions, and an infirmary, for injured rescue victims.
Their internal cabins are pressurized, useful when the vessels are enveloped in heavy smoke, or when countering chemical, biological or radiological attacks.