Throughout the levels you will come across big shiny doors that can only be opened by either a soldier class, commando class or heavy weapons class.
For this cheevo you will need a commando class character like Scarlet.
In Artic mission: Rocket house there is a commando door at the start of the level, keep an eye out to the right side.
Also just up on the left is a heavy weapons door too if you don't have that cheevo.
Both doors are before the forcefield.