Controls
| Action | Keyboard | One-button pad |
|---|---|---|
| Move | W/A/S/D | Up/down/left/right |
| Open panel / confirm | RETURN | Button |
| Select panel entry | W/S | Up/down |
| Close panel | SPACE | Execute an entry |
| Sonar / wait | F / X | Select in the panel |
| Return to BASIC | CTRL+C | Use the keyboard |
The panel offers sonar, recording, quiet-engine mode, waiting, restart, and title. Record from an unrecorded site's cell or an orthogonally adjacent cell. Visit the five sites in any order, then return to your starting point.
Normal movement and waiting cost 1 oxygen; in quiet mode they cost 2. Sonar and recording each cost 2. An extra move caused by a current costs another 1. Hitting a reef damages your hull by 1. You fail if oxygen or hull reaches zero. Time and oxygen do not advance while navigating the panel, viewing a discovery, or giving no input.
Sonar reveals cells within Manhattan distance 6 for six actions; normal visibility is distance 2. Its noise attracts pursuers. Pursuers move every two actions normally, or every four actions in quiet mode. They make contact within distance 1; after a hit, you have four actions of grace.
The instruments show oxygen and its bar, hull, depth, distance and bearing to the next unrecorded site, records collected, engine mode, proximity warning, and sonar state. E/S/W/N in currents indicate the direction they push you. At 30 oxygen or less, !!! and warning sounds draw attention to your remaining air. Proximity warnings also use sound and the display.
Restarting or returning to the title during play asks for confirmation. NO is selected initially. Choose with A/D, confirm with RETURN, or cancel with SPACE.