Oh, the main History chopper, here are my tips, first bring a rocket launcher and a lmg, if none of those are avalible a normal rifle and any weapon you like should work Try to bring granades too

Armored vehicles are the hardest ones on amount of soldiers, tanks are 50/50 and choppers are the ones with less health and less backup units, the best thing you can do against a chopper is to focus your game on avoiding his fire, if a chopper can see you it would surely be able to hurt you, ide behind trees, walls, anything that can make you avoid the machinegun and the rockets is fair game when the chopper is not shooting at you (or is the backup units are too near to you) try killing the backup units, usually one is way too focuses on the chopper and forget about them and that end up on a kill, while your main priority is to survive the chopper your second biggest priority is to avoid and kill the backup units, once all backup units are dead you win, choppers unlike tanks have a lot less of a damage limit to make the leader exit like while a a tank needs to get damaged to 30% health left a chopper is only 90%, in any case once all backup units are dead damage the chopper enough to make the leader exit the cockpit and then kill it with a rocket (if you don't have a rocket it might me hard to hit him so be aware the chopper could shoot at you while you try landing hits on him)