Submachine Gun (SMG) Location
To find the Submachine gun you’ll need to do a couple of things. Head to Ward 13 B2 area and find the locked doors that require a Ward 13 Keycard to open. Once those are opened, head down the hallway to a room on the left and loot the Fuse. Go back to where you came from and go down to B3 area. Place the Fuse into the power switch on the wall to turn on electricity which will allow you to open doors to another area.
Once you swipe the keycard to open the doors, turn the power back off, head through the huge Vent and find the hidden room to the right side. Inside you’ll get the Ward 13 Master Key. Head back to the B2 area which you unlocked previously (where you found the Fuse) and follow the rooms/hallway with the red lights. You’ll end up at the Ward 13 Master room which has the secret SMG.
The secret SMG can be found in the Ward 13 Master room.