Marines do not wear berets, like some depicted in the game. Berets are worn by other branches of the US military, such as the Army.
The layout of the V-22 Osprey depicted in the game is incorrect. The V-22 does not have large side doors in the rear compartment. If they did, the doors would be located under the rotors and extremely unsafe. Passengers in the V-22 enter and exit from a ramp in the rear of the aircraft. This mistake is understandable, since the flight characteristics of the V-22 in the game are also incorrect. The V-22 is shown flying forward with its rotors in the "up" position (parrallel to the ground). In reality, the rotors of the V-22 tilt forward (perpendicular to the ground) for forward flight once the aircraft reaches a certain speed.
In the graphical update, the MP-5 is changed into a derivative of the M-16. However, this weapon fires 9mm rounds. While it is possible that security forces might have a customized M-16 derivatives which can fire 9mm rounds, the military would use assault rifles using N.A.T.O. 5.56mm ammunition or MP-5s using 9mm ammunition.
Valves are shown turning in both directions to close or open, when the standard is to close by turning right and open by turning left.
In the graphical update, the Glock pistol was changed into a Beretta. The Beretta is incapable of firing underwater, yet both are capable of doing so on-game.
The calendar in the room where you wake up says December, but only has 30 days.
Terrain does not make the correct sound when trod upon. For example, grass makes the sound of gravel being stepped upon, and concrete makes the sound of a wood floor being stepped upon.
The P.C.V. is the equivalent of the H.E.V. in the main game. However, a vest is insufficient protection against the hazards faced.
Liquid marked as biohazard on drums shows up as radioactive on the P.C.V.
One of the men in the V-22 has a machine gun belt, even though no one in the section actually has a machine gun.
The black ops people were trying to set a bomb to destroy the facility, but the facility is too big for a single bomb to destroy it.
The Military Police in the boot camp level call Shepard a 'soldier' where clearly he and the other troops in the game are US Marines.
Occasionally several marines, if/when injured, will say 'medic'. Medic is an Army term so they should use 'corpsman' instead (Navy personnel attached to Marine units for medical specialties).
The Marines throughout the game occasionally call Shepard "sir". Shepard is a corporal and only officers are referred as such.