During World War I, fighting was ferocious on the battle lines between France and Germany. Both armies had dug themselves into trenches so much so that there was nearly no movement either way. They sat in the trenches for years on end and simply blasted each other as much as they could. The whole landscape was ruined, bomb after bomb flattened the earth and created a barren wasteland.
This caused a problem, with the landscape being so bare, no soldier could raise himself out of the trenches without being spotted and shot at immediately. Generals were faced with a conundrum, they needed information about enemy movements, but when you have obliterated everything around you, how can a scout hide?
Luckily the French army was quick to find a plausible solution, one thing that the battlefield was not lacking, as corpses. Which meant the obvious answer was to disguise yourself as a dead thing. The idea came about when one of their horses broke away and unfortunately, decided to run straight at the enemy trenches. Most likely the horse was scared by the sound of explosions and gunfire. Unsurprisingly, the horse was shot dead instantly by the enemy.
Someone noticed that a soldier could hide in the carcass, but nobody wanted to hide in an actual horse body. But the powers at be thought the idea may work, which inspired them to create a hollow papier-mache version of a dead horse. In the dark of night, soldiers sneaked out and put the replica horse well close up to the enemy lines.
The sniper inside had his gun and also a telephone wire that ran back to his trenches so he could report on the German movements. The idea did work well, but not for very long, a few days later the German soldier who had shot the horse dead spotted a man climbing out of a dead horse?
It was then they realized it was a decoy and blew it up, even then, the French did try the plot a few more times before giving up.