Sealteam 

Hints:
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Technique is easy. GO SLOW AND STAY DOWN. 
Take your time. Be very sure there are NO 
enemies around before you so much as move 
your team to even a crouch, keep a finger 
on the Q (dive quickly) key when you are in
 anything but a prone position, and NEVER 
RUN (except possibly the last coupla meters 
to the extraction vehicle. 

Also, on OBSERVE missions, make sure you are 
very (at least 50 meters) far (but still in 
targetting range) from the objective you are 
observing being destroyed. Once I was only 30 
mters from the bunker the helicopters were 
destroying and the idiot gunners still cut 
my team to shreds.