Behind the red door is a bridge encased in a glass tube. Equip the BIG MAGNUM and run straight across and into the dark opening in front of you.
In the next room you will immediately be faced with two enemy robots following a brief interaction with Snooper. The easiest way to take out the robots is to run out of their view, which will cause them to simply stand either side of the entrance to the room – this allows you to shoot them from a reasonable distance without even prompting a response. Four shots per robot will be enough.
Note that the robots sometimes drop items – there appears to be no logic to this, the game simply decides if it wants to drop them or not. They are never key items, so don’t worry if you don’t get anything.
To one side of the room there is another cargo vehicle with penetrable rear doors you can remove in order to gain some items.