The Dive Module allows Sophia 3rd, and future incarnations, the ability to move underwater like a submarine instead of sinking like a rock to the bottom like a 150 ton vehicle really should. Unlike the Hover Module, this module doesn't require a secondary energy source to use.
Hard Shell, the boss of Stage 5, holds this module.
The module returns in Blaster Master 2, however, Sophia 4th does not transform, it only gains the ability to move normally through water.
Known as Submarine, the Sophia J-7 automatically transforms into a leaner, more hydrodynamic form when it enters water once this module is obtained.
S.O.P.H.I.A.'s Dive Module is similar to its predecessors, though energy is required to maintain this form.