The most useful role is Medic. You can revive quicker and your special ability allows you to revive multiple teammates at once. You can use one player with an engineer, it is not required but helps to kill juggernauts quicker.
Take a sentry gun, armor and ammo, the sentries can be used when you use a saw on the vault door and a silenced weapon helps get you to the bank undetected.
At the start of the mission, there are a few enemies to take out silently. This prevents you having to fight your way to the bank against infantry and tanks.
After killing these few enemies, make your way to the white container to pick up the saw.
Kill a sniper and take the safest path to the bank.
There will be a huge number of enemies in the bank, counter them and go to the vault gate.
Place a sentry there and try to cut the door with a saw.
After cutting the gate, head into the vault and search all the lock boxes for the device. You will find the crypto private key.
Clear all the enemies there and make your way to the roof of the bank. Blow the enemy chopper with a rocket launcher, so that the banker can not escape.
Move back down and plant an explosive bomb on the door of the branch manager’s room. Place a deployable cover in front of the door.
A juggernaut will come out and start firing, just counter him up.
Head to the roof again and kill two more juggernauts there.
Now it is the time to kill all the mortars around you.
Call the cluster strike to eliminate a large number of enemies and shoot down an enemy chopper.
Head to your chopper now to successfully complete the operation Strongbox.