DOS

Operation Neptune

Introductory premise -- satellite crashes; you must retrieve it

They brought out their biggest boat with the most windows to drop your sub off the back into the Mariana Trench

Title screen

Further premise-establishment

Unique accounts to track different players in two skill modes

Out of your sub-dispenser, and up against an angry -- but predictable -- pufferfish

Get the shiny!

Shooting octopus-ink pellets can blind enemies temporarily

No mere sparkly -- this is one of the capsule pieces strewn through each level.

A basic maths problem needs to be solved to access each capsule component; each one will be set up like this.

Breaking that puzzle...

More of the story doled out, level by level

Further explanation for further puzzles

Visual aids for some puzzles

No aids for others

Small reassurances urge on players to further feats of mathemetical derring-do.

End-of-level -- re-enter the delivery vehicle, return the capsule piece to the surface vessel. Lather, rinse, repeat.