It began in the Bosnia mission in 1995-1996. There was also some during the first Gulf War. Currently, there is uranium in Afghanistan.
The bullets of the heavy machine guns on tanks are made of depleted uranium. Depleted uranium is a metal with a density that is much greater than the density of steel, and so it is better for piercing through the enemy vehicle's armour. Given that depleted uranium is waste from nuclear power plants, it is not very expensive.
There is one problem. When the shell hits the enemy vehicle, it fragments into microdust. This radioactive microdust, when it is breathed in, goes through our lungs, then through our blood system, and ends up taking residence in the bone marrow. This creates a degenerative illness that is enormously similar to multiple sclerosis.