We're Gonna Need a Bigger Ship Achievement in Halo: The Master Chief Collection

This achievement can be earned on the Easy difficulty (or higher).

This Easter Egg involves a couple prerequisites and, while it's technically achievable solo, is best done with another player. The prerequisites are as follows:

• Keep one Falcon intact
• Obtain a Jetpack in the Hospital
• Obtain a Banshee (you will need to hijack one; the best way to do this is to, after obtaining a Jetpack, fly your Falcon over an enemy Banshee and then exit the Falcon and perform a hijack mid-fall, using the Jetpack to aid in your directional descent/ascent, if needed)

Once you have the Falcon, Jetpack, and Banshee, you will need to fly both vehicles toward Club Errera. Around this area, there is a tall building west of the Club. The player inside the Falcon will need to land their vehicle on the rooftop and, quite trickily, use the Jetpack to locate a hidden button on the underside of a lower floor.

NOTE: It's important for the player inside the Banshee to remain inside the vehicle; the Banshee has the tendency to despawn/disappear if left unattended for too long.

Once the hidden switch has been activated, the player who activated the button can fall to their death and spawn on the second player (near the Falcon, of course). Now, one player will need to fly through a very large "ring-like" bridge structure in the distance (please refer to the video for its exact location). The player flying the Falcon through this structure will, after a short delay, transform their vehicle into a Pelican. After this happens, the other player can then fly their Banshee through the same structure, in turn morphing it into a Phantom and unlocking the achievement for both/all players within the game.

For a visual aid, since this may seem very vague and complicated to follow, please refer to the video guide below, courtesy of Halo Completionist.