go to options and click all guns availible and then these guns will win the game for you. These are in order of how useful they are. Primary gun: 1)Rocket launcher 2)Napalm launcher 3)Flamethrower
all of you people who need to use the future weapons to win SUCK at the game. I find it almost too easy even to just use the best gun from that period. the only 5 or so weapons that you really need are:
Past:
M1 Garand: super accurate, even if it takes a few shots to kill.
The funny machinegun with the clip on top: Has a bayonet... all of the other jap guns suck.
BAR: 2 shot kill, super accurate.
AK 47: half decent... all vietcong guns suck.
Present:
Kord 14.5 mm (1 hit kill on normal humans, deadly accurate)
FN SCAR (the grenade launcher on it can wipe out most of the enemies on a given level, and it can kill in 2 shots, accurate)
Future:
Gauss rifle (2 hit kills on aliens/monsters, super accurate)
and, of course, good old Frag grenades, unless your on super-hard difficulty the shrapnel can kill in one hit, across the map.
and, one extra: The minigun. this needs no explanation.
So, just use the good weapons from your period and frags, don't be stupid and you can win easily. also, for a good chalenge: only use the gun you get auto-assigned (usually isn't very good)