We're Gonna Need a Bigger Ship
From Halopedia, the Halo wiki
We're Gonna Need a Bigger Ship is an achievement in Halo: The Master Chief Collection. It is awarded by flying both vehicles in the flyable Pelican and Phantom Easter egg on the level New Alexandria in Halo: Reach.
To unlock this achievement, see Halopedia's guide here. To ensure the achievement unlocks, both vehicles must be flown.
The name of the achievement is a reference to the line "You're gonna need a bigger boat" from the classic 1975 film Jaws.