Logistics are the key to any military operation. You cannot field an army to fight your battles without logistics. Some things are obvious, such as fuel and ammo. Others aren’t quite as obvious, such as moving worn out vehicles and weapons back to the rear to be repaired and refurbished.
The Army of course, has a massive logistics system. This system encompasses far more than merely providing supply items, but that is a major part of it. The Army generally puts supply items into one of 10 classes of items:
Class I- Food
Class II- Clothing, individual equipment, tentage, organizational tool sets and kits, hand tools, unclassified maps, administrative and housekeeping supplies and equipment
Class III- Petroleum, oil and lubricant products
Class IV- Construction and barrier materials
Class V- Ammunition of all sorts
Class VI- Personal demand items
Class VII- Major end items (like a complete tank, or a truck)
Class VIII- Medical supply items
Class IX- Repair parts for class II and VII items
Class X- Material support to nonmilitary programs
Almost all items that the Army might ship will fit into one of these categories (interestingly, potable water isn’t in one of these categories. You’d think it would be in Class I, but you’d be wrong. Water is its own thing).
The supply system works slightly differently for the Army in the field than it does at a base in the states. Forces in the field are said to be deployed to a theater of operations. The theater is run by one of the geographic regional commanders. For instance, Gen. Petraeus ran CentCom, or Central Command, which has responsibility for Iraq, Afghanistan and the rest of the Middle East. CentCom is responsible for getting supplies into the theater and running all the support operations in the area.
Let’s take an example of a company that needs a repair part for a Bradley. One of the metal road wheels on one of the Bradley’s has been damaged and needs to be replaced. The driver fills out the request for the part. Now, it would take quite a while to ship a roadwheel all the way from the states. Plus, that’s a part that needs to be replaced fairly often. In fact, the company has some on hand. What happens is that the company issues a roadwheel to the driver and then orders a replacement. The same process occurs all the way through the chain of supply, this order being consolidated with others as it goes up the chain.
There are similar processes for most items of supply. Back in my day, we did all this with paper and pen. Towards the end of my time, we started keeping track of orders on computer. Now the same computers that allow units to track each other on the battlefield and transmit orders can order parts and supplies.