Put this on today, and im running around shootin stuff, and i have run out of ammo, how i locate and reload the main gun you at the start of the game, i have consulted the indtrucyion booklet without success !!!
They often have walkthroughs where they will describe what to do (reloading the main gun sounds like it's got to be one of them).
Finally you could try searching for some Youtube "Walkthrougs". Here you'll see people playing the game and through a little "monkey see & monkey do" you can often sort out what you need to achieve yourself.
Ammo for the walrus can be found by looking at the mini map and locating an ammo dump,just drive up to it and it reloads automatic or you can dock with carrier and that re-arms,the mantas have to be docked to carrier to re-arm,ammo for the foot soldier has
to be picked up off dead enemies. hope that helped.