The goal of Operation Neptune is to guide a small submarine through a variety of undersea caverns, collecting pieces of a ruined space capsule. Like other games by The Learning Company, Operation Neptune is educational and was intended for players age nine to fourteen.
The game is divided into five zones : Dragon Reef, Fossil Trench, Limestone Ridge, Sea Forest, and Hammerhead. Each zone contains three "levels", called sectors (although the hammerhead zone also has a "final" sector, where there are no maths problems, but one hit from a sea creature will send the player back to the start). At the end of each sector, the submarine approaches an undersea supply station. There are two completely unique sets of levels, Voyager and Expert, each with a different story that is recovered along the way.
The player pilots the submarine, named the Neptune. Throughout the game, elementary school-level mathematics problems are posed, in the form of scientific situations that might concern a submarine pilot in real life. (For example, the sub's ballast may need adjusting, and this becomes an arithmetic problem.) In each sector the player will face three randomly placed math problems, as well as one problem to open that sector's data canister, and another to open the combination lock on the supply station.
Source: Wikipedia, "Operation Neptune (video game)", available under the CC-BY-SA License.