Hajile was created by the same minds that brought you the Great Panjandrum, and in terms of explosive failure, it reaches that high bar. An early retrorocket design, Hajile was created with the hope of using a rocket to slow the descent of supplies dropped from planes. This idea was recently used successfully to land the Curiosity rover on Mars (similar to image above), but the Hajile project was anything but a success.
The Hajile project was named as the reverse of “Elijah,” who ascended to heaven on a column of flame in the Bible story. Hajile was originally tested on concrete blocks with rockets strapped to them. When a dangling weight below the block hit the ground, the rockets would fire to slow the descent of the payload.
However, the first three tests were disasters. Twice, the rockets failed to slow the descent enough. On the third test, too much fuel relaunched the payload several dozen feet in the air.
The device was tested until it was successfully used, and eventually, two jeeps were donated by the United States Navy for real-world testing. One crashed into the ground at 48 kilometers per hour (30 mph), and the second was successfully landed with minimal damage as long as you count an upside-down jeep as a success.
Deeply unreliable, the project was shelved as World War II drew to a close