This is a more subtle way of handling this mission. First climb up the ladder and run towards the train block infront of you. Now hit sneak mode with your knife drawn. See the nearest warehouse? At the bottom right hand corner(should you check the map), there is a guard with his back to you should you sneak up to him from the train block. Slashed him and take his MP5 & clothes. Run ahead and in between the 2 warehouses. See the other guard patrolling with his back to you, take him out. You can leave his body there(in between those warehouses). Now quickly run towards the northwest( map reference). You should see a gate and 2 guards.