For relief operations following natural disasters in remote areas, or when trying to get supplies and troops into conflict zones, the military may not have the option of landing a cargo plane on an airstrip. In those instances, they rely on their own form of UPS: The military air drop.
The bulk and number of items dropped, and the rapid succession in which they can be dumped out of the plane, is pretty staggering. To see what we mean, fast forward to 1:47 in this video of a 2011 drop over Afghanistan. (If you watch closely, you can see at least one pallet with an apparently failed parachute, as it appears to break away from the pack and plummet downwards.) By the way this is what's called a Gravity Drop, where the pallets slide out of the plane like sleds, propelled by simple gravity, before the chutes deploy.
If you want to get a sense of what that looks like from the ground, fast-forward to 0:57 in this video, which is of a relief supply air drop over Haiti during 2010's Operation Unified Response:
What's amazing is just how big an item you can safely drop out of an airplane. Here are some Humvees getting the gravity treatment, as demonstrated by the 517th Airlift Squadron, accompanied by Airborne Infantry from the 3rd Battalion of the 509th:
Drops needn't be done over land, of course. Here's footage of a C-17 dumping supplies and a bunch of Navy guys (from Naval Special Warfare Group Four and Special Boat Team Twenty) somewhere over the Atlantic. With the gear, this is what's called an Extraction Drop, where the parachute is deployed out of the back of the plane first, and then yanks the package outside:
Neither do air drops need to take place during daylight hours. Here's footage of a nighttime drop from the 816th Expeditionary Airlift Squadron over Afghanistan, as seen through their night-vision goggles:
Dumping and jumping is the fun part of the process, but before that can happen a bunch of crewmen have to make fastidious preparations. Gear has to be loaded, tied down and inspected. The plane floor is equipped with rollers to help the pallets travel in and out. Interestingly enough, the pallets, which you get a look at in this video of preparations and subsequent drops over Afghanistan, appear to be made out of really thick cardboard.
What do you think is the heaviest item that can be successfully dropped? Believe it or not, it's a 42,000-pound tank!