Bus

"Officially, it's an Airborne Mobile Command Station, but we call it the Bus."

- Leo Fitz to Skye

The Bus (formally known as the CXD 23 Airborne Mobile Command Station officially designated as "S.H.I.E.L.D. 6-1-6".) is a specialized  owned and modified by S.H.I.E.L.D.. The planes were in heavy rotation from the 1980s to the 1990s until S.H.I.E.L.D. built the Helicarrier. Following, the Battle of New York on Director Nick Fury's and Agent Phil Coulson's orders, the Bus underwent a complete overhaul. It served as a flying command center for Agent Phil Coulson and his team before being stolen by Grant Ward. Coulson's team reclaimed it during the Battle at Cybertek.

Capabilities
The Bus is a specialized Boeing C-17 Globemaster III modified to serve as an 'Airborne Mobile Command Station' for Agent Coulson's personal S.H.I.E.L.D. team. In addition to the common features of the Boeing C-17, the Bus has an additional pair of engines and half-length wings located at the tail section of the fuselage, below the conventional, elevated tail section. Additionally, the six engines are able to pivot up on each wing, allowing them to be angled at the ground, giving the Bus Vertical Take-Off and Landing (VTOL) capabilities. This, along with an advance set of "air brake" panels on each wing, gives the Bus greater aerodynamic and flight capabilities, such as allowing it to preform a full, mid-air stop before changing direction to peruse a new flight plan. On top of the Bus are mounts and an access way to allow a single S.H.I.E.L.D. Jump Jet to dock with, and later separate from, the Bus in mid-flight.

The Bus possesses some provisional offensive/defensive capabilities in the form of two retractable cannon turrets, located at the junction of between each main wing and the fuselage, which are capable of shooting down enemy aircraft. The Bus also has a form of large, long barreled cannon mounted to the front underside of the fuselage that allows it to attack targets on the ground while in VTOL flight.

The Bus possesses advanced satellite, radio, and other wireless connections as well as a strong computer system that could connect to S.H.I.E.L.D.'s operational databases, as well as any other secure databases or other resources across the internet. This allows it to receive any mission briefings sent down from the Triskelion or the Hub. More prominently, the Bus' flight plan can be remotely altered by anyone with a high enough clearance level from any major S.H.I.E.L.D. facility, even forcing it to return to base. Likewise, several of the Bus' functions can be remotely controlled by certain S.H.I.E.L.D. vehicles, such as the SUV that many agents use in the field, primarily allowing its cargo doors to be opened in the case of a quick retreat. The Bus also has encrypted lines to communicate with any agent based at a S.H.I.E.L.D. facility, as well as any agents or other allies in the field.

While the majority of a conventional C-17's interior is open cargo space, the Bus has been modified to suit the needs of Coulson's S.H.I.E.L.D. team, including three passenger decks replacing the forward cargo space. The passenger space includes living quarters a commons area with a mini-bar, a briefing room, a number of various storage rooms, and a private forensics and research lab to accommodate Agents Leo Fitz and Jemma Simmons. The highest deck of the Bus, near the front of the plane also houses agent Coulson's personal office. There is also an interrogation room/holding cell known as 'the Cage', whose walls are built with silicon-carbide Vibranium alloy. The Bus retains a small cargo area at the rear of the plane where the team's SUV is stored along with Coulson's personal car, Lola.

The Bus also contains space near the front of the plane that can accommodate the addition of an interchangeable modular room, such as the Medical Pod that was used by Skye while she was recovering from a near-fatal gunshot wound.

The Bus' computer systems independently stores all of the specs and information on the many operations that Coulson's Team have been involved with, including the various items and individuals that the team has come in contact with, in a separate data line individual from that of the main S.H.I.E.L.D. database.

Originally, the Bus did not have the stealth technology that some vehicles such as the Helicarrier and the Quinjet possess, so it compensated by flying under radar. After Coulson became the director of S.H.I.E.L.D. and stole a Quinjet, he had his scientists add cloaking technology to the Bus.