Penetration of the Front Base is the sixth mission of Metal Slug: 1st Mission.
The Hero infiltrates a Rebel base. The mission has two pathways that merge near the exit to the moving platforms. Entering from Mission 5 starts at the bottom path, and the Hero jumps on exploding bombs to reach higher platforms. Entering from Mission 7 starts at the upper path; the Hero traverses down the base.
The last hallway takes place on moving platforms suspended over a pit. The platforms stop and split open in the middle of their track. This requires the Hero to jump over at the precise moment so he can land when the platform closes again. Entering the exit leads to a battle with Macba.
- Complete Mission 5 (Pursuit of the Transport Train).
- Hidden Route of Mission 7 (Discovery of the Front Base).
Mission completion proceeds to Mission 9 (Discovery of a Secret Passage).