The -400 airliner was removed due to certain aerodynamics issues. However, the military variant here was not affected.

So, this is a large, four engine transport which is totally not a cross between a Boeing E-4 and a KC-33A.

List of modifications made in case I forget it again:
Stretched upper deck
Stretched fuselage
Flaps are 55 degrees? 60 degrees?
Replaced nosecone
Added a radome to replace the accursed black and white dishes.
Modified landing gear. Don't ask
Rear boom added

Instructions:
Activation group one and throttle ~ Engine one
Activation group two and throttle ~ Engine two
Activation group three and throttle ~ Engine three
Activation group four and throttle ~ Engine four

Activation group five and fire weapons key/alt ~ Engine one thrust reverse
Activation group six a and fire weapons key/alt ~ Engine two thrust reverse
Activation group seven and fire weapons key/alt ~ Engine three thrust reverse
Activation group eight and fire weapons key/alt ~ Engine four thrust reverse
Activation group one and fire guns/space ~ lower boom
VTOL slider ~ Pitch boost control.