If you're after all, if not most of the achievements in the game, stick with the default dual pistols you have until you complete this mission. Doing so will unlock the Double Trouble achievement. Later in the mission you'll find dual SMGs which can also be used as long as its dual wield.
Objective: Escape with Dr. Clarke
The first intel in the mission can be found as soon as the mission starts. Check the table to your right to find it.
Numbers Intel 1/3
Climb up the ladder and fight your way through the tight hallways. Head to the roof and let the others jump first. Sprint to the edge of the roof and jump to land on the building across. Clarke will reveal a stash of weapons behind the fridge so grab anything that you need then continue fighting your way through the building.
Continue outside and follow Clarke. The enemies here will be limitless so don't attempt to fight them off. Just kill the ones along the way and follow the path until you reach a vent where you'll jump down to safety. Get out on the other end of the vent then kill the two pursuers on the ground. Continue following the path until you find an inclined roof where you'll slide. Slide down and kill the enemies. The next intel is located right in front of you, behind the porch wall. See the video below:
Numbers Intel 2/3
Once Clarke opens the small gate, keep jumping down the roof then go inside the marked door. Enemies will burst right in so take them out. Continue fighting your way through again until you reach another secret ammo cache. Spetnaz soldiers will start pouring it so dig in and fend them off.
Objective: Escape with Clarke
After that, follow Clarke again outside and jump to the other roof in an attempt to save him. Make your way down by jumping from roof to roof. Once you see a scaffolding in front of you, jump down and look for the intel behind.
Numbers Intel 3/3
Continue jumping down and shoot the last set of enemies then ride the van to complete the mission.