The Blue Marine is a specially design submarine used by the Star Fox team. It is used on Aquas to explore the underwater regions that the team's other vehicles can't transverse. The craft bears some similarities to the Arwing, such as freedom of movement around the screen, but handles quite differently.
Much like the Arwing, the submarine has a front mounted laser cannon that can be upgraded to twin and then hyper lasers (if the player enters Aquas with upgraded lasers then the craft will already have them). However, this craft is incapable of charging plasma bolts with its lasers.
The Blue Marine also lacks the ability to use smart bombs. Instead, the B button makes use of an infinite number of torpedos, which in a way act similarly to plasma bolts in that they produce small explosions that can take groups out and that they lock onto targets. They are different in that they move more slowly than plasma bolts and that the player can change the locked on target while the torpedo is on its way by pressing B while focusing aim on a new target. The submarine is limited to firing one torpedo at a time, and must wait until it has exploded before it can fire another.
Boost and brake functions are included in the submarine as well, draining the boost gauge when in use. Unlike the Arwing it cannot perform any flips. The Blue Marine can bank to the left or right and even perform the same kind of barrel roll, which spins the craft and projects a temporary shield that deflects laser fire. You'll find yourself performing this a lot more often than in the Arwing as enemies appear a lot more often from other places than just straight ahead, constantly coming in from the sides and even from underneath.
 Star Fox 64
The Blue Marine's only appearance. The submarine is only used in Aquas, since neither the Arwing nor the Landmaster can enter the deep waters.