A French trench during World War I, 1918. This photo is likely staged, as it depicts a soldier peeking above the top of the trench - a very dangerous activity! Credit: Woodrow Wilson Presidential Library / Flickr Creative Commons

Picture it: You're a young soldier – maybe 19 or 20 – sitting six feet below ground, legs stiff, scared for your life. A few rats scuttle by, mud and filth are all around you, and there's gunfire in the distance that never seems to stop. For hours – maybe even days – time seems to stand still. And then, chaos.

Many of the inventions born of war -- from poison gas to tanks to the trenches themselves -- only serve to increase casualties. But there can also be some ingenious, helpful, and lasting creations that come from crisis.

The seeds of this particular invention were planted in two wars: the Boer Wars of the 1880s and WWI. In combat, British soldiers needed to coordinate troop movements expertly and precisely, and they needed to do it fast.

So what ingenious innovation helped them? For the full story, tune in above.