"Oregon Iron Works, a small specialist manufacturer has designed and produced a series of special forces infiltration boats currently employed by Israeli special forces and USN SEALs. The original patents were filed in 1990 but the first boat, now known as Alligator class, was not produced until the mid 1990s and to a significantly modified design. After testing with US forces the Alligator was transferred to Israeli military. ...
The rear cabin is removable, and the boat is often shown with large crew railings attached which alter its general appearance and make misidentification easy. ...
Although the boats are somewhat publicised by their manufacturer, they are not well reported and have been subject to several "mystery stealth boat" articles on the web. ..."
"covertshores.blogspot.com" website, June 21, 2010, "Alligator & Sealion stealthy semi-submersibles.
"For about a decade there have been sightings of some very peculiar high-speed watercraft patrolling up and down the Columbia River between Portland and Vancouver. It just so happens that these phantom vessels are some of the US Navy SEALs newest toys.
The origin of these boats remains somewhat shadowy, but it would seem that they evolved from a concept initiated by the Israeli Special Operations community in the late 1980's. Patents filed in the 1990s show the design would become "the Alligator," a semi-submersible, high-speed special forces delivery, extraction and reconnaissance craft that features a very low radar cross-section. All known accounts state that the Alligator was first launched in the mid 1990s and was said to have been tested briefly by the US Special Operations community before being delivered to Israel. The number of alligators built remains a mystery.
The already low-slung Alligator has the ability to lower its draft to the point where the cabin windows sit right above the waterline via flooring ballast tanks located on each side and below the boat's main cabin. This results in the boat not only being very hard to spot on radar but it is also challenging to spot visually. The streamlined hull and low drag design, along with some powerful water-jets, allow it to move at high speed, especially when its ballast tanks are empty.
Although I have had some trouble getting a confirmation on it, it seems that Oregon Iron Works, a locally well known metal fabrication firm, has been involved with building the Alligator since its inception and continues as the prime contractor for constructing not only the Alligator Class but also its follow-on Sealion and Sealion II Class. "
"foxtrotalpha.jalopnik.com" website, May 29, 2014, "Unmasking The Columbia River's Mysterious Stealth Boats", written by Tyler Rogoway.