The second optional mission is to go behind enemy lines, once again all by yourself, to blow up about a half dozen enemy tanks single handed
sneak up the hill, kill the guard in the valley, put a det pack on the first APV, climb up the hill detonate and get your rpg out, shoot other 2 tanks while the soldiers are near them (explosion will kill them too) then there are only a few left to shoot. run back to your boat where you will see a heli blow it up... then it gets tough.
I loved that mission; it's a learning mission, it forces you into almost every type of encounter. This was the hardest one for me, but you learn alot and makes the rest of the game somewhat easier. You will have to search the dead and take thier weapons, learn to use grenades and your gun is amazingly acurate too.