This is the simplest and quickest compost bin to build.
The necessary materials can be obtained for free anywhere.

I designed this with The Pentagon in mind, as a way for our armed forces to deal with their organic waste without burning or trucking it, both of which expose our troops to harm.

Setup and knock down is very quick and easy.
This composter will eventually compost itself, which is a good thing, since it's made from waste materials and is so easy to build.

Want your compost quicker? Try a Compost Tumbler

Step 1: Gather Materials

It took me about a minute to find the materials in our dumpster area here on the base. Here's what you need:

5 identical wooden panels. If the ones you find are too big or small, cut them down or nail on another section. I found some 40" wide chunks of weathered plywood of varying lengths from packing crates. Don't use pressure-treated wood. For anything.

Rope, cord, or wire. I found a 20foot chunk of polypropylene rope and some smaller pieces of polypropylene rope.

Paint: Optional. Since my composter is intended for the military I chose olive drab. Since I'm on a former military base which is now a superfund site, all the military shades of paint are very plentiful in orphan piles.

Step 2: Trim the Panels

The plywood I found was pretty rotten around the edges so I pulled the nails and sawed an inch off three sides. Then I scored each panel at the same height and sawed them same.
I ended up with five panels 37" (about one meter) square.

The dimensions are not critical at all. Make yours big enough for the quantity of compost you'll get, or to fit in the space you have available.

Step 3: Drill Holes

Drill two 1" (~25mm) holes in each side edge of each panel.
I stacked them up and drilled them all at once.
The spade bit, usually my favorite, didn't work well.
The rotten wood fibers wrapped around the edge and clogged it.
A different bit with a feed screw at the tip worked better.

Compost needs air to decay properly. If you want more air to get to your compost drill more holes in the sides.

Step 4: Paint - Optional

Paint is optional. Think about whether you actually want to paint it.
This composter will eventually compost itself and join your soil, your food and your own body.

I chose Olive Drab (O.D.) so as to not give away the position.
Choose the camouflage pattern that matches your terrain.
"Dazzle paint" would be great for a marine setting.

I found an orphan can of O.D. latex paint and slobbered it all over the panels with a roller and a small brush for the inside of the holes. I painted both sides which is totally unnecessary, but coffee demons made me do it.

Get a real paint lid pry-tool from your nearest paint store and don't mess up the lip of the can. That way it won't dry up in the can so quick.
I'm a big fan of misusing tools and adapting one thing for another, except for those paint can tools. Don't use anything else for that. Get the real tool. It's free.

Step 5: Deploy

Set up the panels leaning corner-to-corner like a house of cards.
Tie the corners together with cord or wire. I used my long piece of cord running it through all the upper holes.

I tied the ends together with a "trucker's hitch" and drew the cord tight.

Step 6: Compost Away!

I put an oyster mushroom starter in my composter to help break down hydrocarbons and other chemicals. There are a lot of such chemicals spilled here on the base from fueling and maintaining aircraft. JuniorLee gave me the mushroom starter from a project she worked on in New Orleans after the disaster.

KEEP YOUR COMPOST WET
Your compost needs air and water to work properly. It doesn't need to be soggy, but make sure your compost doesn't dry out. It will get hot from decomposition and that will tend to dry it out. Soapy water or rainwater is fine.

ANIMALS
If you want to keep animals out of your compost put a weighted board or chickenwire over the top. If they're very motivated you may need to nail chickenwire around it and set it on chickenwire. Depending on what the animals are you might not care. Their guts will break down the plant matter faster than anything else.

HUMAN MANURE
If you want to compost human manure, read the book Humanure Handbook. You'll want at least two composters so you can let one sit inactive for several months after the last addition before dumping and spreading it on your garden.

Step 7: One Year of Evolution Later...

I've moved the composter onto a pallet so it can be moved with a forklift.
It's now square so it could fit on the pallet better, and so the fifth wall panel can be used to cover it in the rainy season.

The compost was getting way too wet in the rainy season. So it needed a lid.
Some years we get all our rain in three months, and then we don't get any rain at all for six months.

In the rainy season and right afterward, the grass and weeds grow like crazy. We get a lot of grass clippings and weeds to compost. In the dry season there was a watering ban, and everything turned brown and stopped growing. So then the compost began to be mostly food waste. There was a thriving worm colony in the compost, but they couldn't keep up with the food waste. That led to fly and smell problems. It was located right under some open windows. That wasn't good for the people inside the windows. So the compost needed to move away and to get mixed more.

I've just added a Compost Tumbler as a first stage composter..
I'll probably add another square bin so there'll be a convenient supply of old compost for gardening and for adding to the fresh compost.