Call of duty world at war ?

Im trying to get platinum ive been trying this mission for like 2 years it's not funny -.- no i just can't do it it's the second last mission on call of duty world at war i cant do it because there to much grenades constantly grenades grenades grenades omg is there meant to be that many it's on veteran but still it's stupid -.- i can't even get past destroy all 4 aa gun thing's