Discovery of the Front Base is the seventh mission of Metal Slug: 1st Mission.
The Hero finds a Rebel base. The building is a maze with doors that lead to dead ends or to early parts of the mission. The normal way to get out is finding a POW waving on top of crates. The hidden route is dropping down a specific gap and traversing over blocks that pop out from the background. The player must be careful when riding the elevators as incorrect positioning crushes the player from the ceiling.
- Incomplete Mission 1 (Hurry On).
- Mission Complete: Proceed to Mission 8 (Forced Escape).
- Hidden Route: Retreat to Mission 6 (Penetration of the Front Base).