Level 16. Subpen 7

Start in front of a submarine and kill the ninja on top.

Jump on the sub; the first 3 blast doors will open. Kill the ninjas by shooting barrels, checking each area for items.

As you move to the other end of the sub, the last two blast doors will open with ninjas and fuel tanks. Blow up the tanks to kill the ninjas.

Grab the BLUE KEYCARD at the most far-right blast door opening, at the top of the crates.

The blue key door is in the first right opening you came through. Use the BLUE KEYCARD on it and go through.

Follow the corridor, killing enemies, and enter the door ahead into a large area.

A grey ninja will be pumping grenades at you near a mechanism that requires the YELLOW KEYCARD.

From your entry point, head left, then north, then take the first left, and then head north until you reach a small ladder with tanks and ninjas on the top level.

Blow up the barrels to generate the YELLOW KEYCARD.

Grab the yellow keycard and return to the mechanism. Use the key on the mechanism and hit the switch.

This opens the Restricted doors on the other end. Head there before they close.

To the very East, the RED KEYCARD is on the crates. Grab it and kill all enemies.

Head back to the very West door and go through. The red key door is right ahead.

Use the RED KEY on it to open it, revealing the end switch.

Approach the end switch to be transported to a cell.

Walk forward to end the level.