The mission is 'The Escape' and this is a step by step walkthrough which should net you all of these:
• Stake a claim: gold medal any co-op mission
• Well done complete a co-op mission
• Bullet proof complete a co-op mission without dying
• 2 guys 1 co-op 1 mission
• Friends indeed complete a co-op mission without anyone dying
There are extensive notes and a commentary on the video link and it is definite walk through of the first level so if you want to experience it yourself I'd suggest coming back to it!
Anyway, here's the link and I hope this helps!