Did You Major in Marine Bio?
From Halopedia, the Halo wiki
Did You Major in Marine Bio? is an achievement in Halo: The Master Chief Collection. It is awarded for finding a group of hidden marines on Exodus, requiring difficult traversal out of the AA battery location back to an area where the player defends UNSC Army troopers from Jiralhanae during the Falcon gunner section of the mission. The group of marines may or may not be present, But regardless, you will earn the achievement anyway.
- The achievement is a play on marine biology and Marines.
- The achievement is a likely homage to players who traversed out of the map, most notably performed in a Generalkidd video from 2010 on YouTube.