We’ve seen a similar video before, and couldn’t resist stealing this one from the Armorer over at The Castle. There is, not surprisingly, a good deal of NSFW language, so you might turn down the volume, or wait till you get home to watch.
What we see is a mortar team firing their 120mm mortar at Anti-Coalition Forces that are (presumably) attacking their Combat Outpost. Since the idea is to suppress the incoming fire, they are laying down both High Explosive and White Phosphorus rounds on the enemy. The HE of course blows up real good, and while the WP may cause casualties, the primary effect is the dense white smoke makes it hard for the enemy to aim their weapons.
Note the professionalism of the crew. Just as soon as the fight is over, they start clearing up the pit, counting their ammo, cleaning their tube, and generally getting everything set for another round. Impressive.