Cod black ops help!!

Sup guys i've been trying to get more black ops trophies lately so I tried to beat the campaign of veteren and man is it hard. I made it to thefourthmission ( Executive orders) just after you blow the space rocket thing upand im pretty much screwed are there any tips on how the hell to beat it on veteren. I go in slowely and take my time so I don't get owned but then I think they keep respawning.

I used a thew smoke grenades and then beat the mission then I wait for a trophy to pop up but NO. Man am I pissed off I beat operation 40, vorkuta and executive order on veteran and get nothing for it. I was supposed to get a trophy all that for nothing.

That has to be one of the most difficult missions in the game. Everything else takes patience, for here you simply need to run until you get the check point around the corner. Flash bangs help alot. Once you beat that the rest of the game is a cake walk.