In this level, if you unlocked the lasers in the previous level, DO NOT USE THEM. They do not have the firepower to take out the cannons on the side of the train. Instead, use the HEMP Rockets...a full barrage of them can completely destroy a cannon. Also, do not worry about the chaingun that comes out of the back of each train car LAST...take out the cannons, because they can almost completely destroy the interceptor (car) in ONE SHOT. Luckily, they are incredibly inaccurate, and if in the correct spot you can dodge their shots (beware, they are somewhat seeking). As for the aux. weapon, i would recommend using either the HPCP shields (purple) because, if used properly, can avoid you taking any damage; or, use the heavy armor (unlocked with the lasers, hopefully), which makes the chainguns do almost no damage whatsoever...unfortunately, the cannons can still take you out in one or 2 hits...beware.