Captain yout submarine through dangerous water to reach the enemy port then destroy their cargo ship. Among the many obstacles you must avoid are mines, submarine nets, and aeroplanes.

How to play the game:

Stage One: To complete the first stage of your mission you must guide your vessel through the submarine nets. You must not touch the nets or the mines which are between them. You cannot reverse your submarine, however you may pause at any point to let a mine pass by. You must negotiate  this stage of the game before your limited air supply runs out. Your submarine cannot travel at too great a depth or it will be crushed by the pressure of the water. The safe maximum depth is indicated by the ‘limit’ triangle at the top of the screen and your actual depth is shown by the strip below it.

Stage Two: The next stage of the mission is one of survival. Enemy ship and aeroplane try to bomb you out of the water. The ship drop depth charges which you must avoid, and when you rise to the surface they fire torpedoes at you and the aeroplane drop bombs on you. Use the fire button to shoot torpedoes at the ship when you are on the surface of the water. Your air supply is limited, so you must keep returning to the surface in order to replenish it. If you fail to do so you will be destroyed when the air supply runs out. When you have destroyed 10 times the ship you automatically move on the third and final stage.

Stage Three: To complete your mission you must destroy the cargo ship which is sailing into port. The bow of your submarine can be seen at the bottom of the screen as barges float back and forth between you and the target cross on the ship. Position you vessel then fire between the barges to destroy the ship.