Get through bullet-proof glass in training.
When you are in the training level and in the live fire range get to the bit where you have the smoke and the flashbang grenades.
Throw the flashbang grenade at the ammo window and the window will smash! You can then do the duck jump (which you learnt how to do earlier) into the room.
Sadly you can't get any grenades or guns SHAME! :'( and you can't hurt the guards unless when you had the weapons you shoot at them through the hle in the bottom the the bullet proof glass!
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