Although Starfishman is a strong swimmer, he realizes that he needs a special vehicle to help him move around the ocean and accomplish his missions. With help from Uni Chin, Starfishman scavenges for parts from the Pacific Marine Institute wreckage and builds himself a submarine of his own design.
Starfishman's submarine was an absolutely mandatory vehicle that Starfishman would use in practically every episode of the comic. Starfishman can breathe underwater, but he needed a vehicle to move quickly through the water and platform for sensors and tools to conduct scientific research. The first designs had a pentagonally-radial symmetry, just like a starfish, with a large conning tower at the top. The early designs were fairly simple so not much other detail is shown.
In Starfishman: Shark Finners, Starfishman uses his submarine to scan a fishing boat and determine its identity despite the fact it has turned off its Automatic Identification Signal (AIS). There are several other sensor readouts which cover the temperature and chemical composition of the water, the depth and high resolution 3D scan of the ocean floor, and many other important displays.
Starfishman's submarine is primarily a research craft, so its main technologies involve sensors and other exploratory functions. It has 3D displays inside which are based on the research from Dr. Quatel of The Pacific Marine Institute. Much of the tech on board has been scavenged from the wreckage from the PMI, which was destroyed in the catastrophic accident. Starfishman is wary of integrating the meta wave generator, as he is concerned that it was originally designed as a weapon. At lower power levels, it does make for an extremely precise scanner and communication device, so he eventually does integrate it into the sub's systems.
The sub has no torpedoes or other destructive weapons, but Starfishman is always tinkering with its capabilities. It's possible that the sub has defensive weapons such as a sonar emitter or EMP pulse, but we'll all have to follow his stories to find out!