The Super Soaker, as it's known to millions, is a little more advanced than your typical water gun. This high-powered weapon has drenched many backyard warriors and revitalized the toy gun market.
And unlike his work in the design of three NASA space probes that earned him a plaque, this homemade gadget turned the rocket scientist into a millionaire.
"Obviously, it was a cut above anything that was available but I never expected it would set the standard worldwide in water guns," said Johnson, 49, sitting in his suburban Atlanta research and development office.
A native of Mobile, Ala., Johnson's career had its start in 1968 when he won a state science fair competition with Linex, a remote-controlled robot he built using batteries, compressed air and tape reels.
"Back then robots were unheard of so I was one of only a few kids in the country who had his own robot," he said.
Not bad for a black kid who was told while growing up in the South that he didn't have what it took to be an engineer. Although disheartened, Johnson persevered, earning a bachelor's degree in mechanical engineering and a master's in nuclear engineering. He holds 49 patents, and is working on more inventions at his own research firm.
As an engineer at the National Aeronautics and Space Administration's acclaimed Jet Propulsion Laboratory in Pasadena, Calif., Johnson worked on Voyager, Mars Observer, and Galileo.
"I came up with the idea of a memory keeper power supply that would operate even if there was a short circuit aboard the spacecraft," he said of his work on Galileo, which was launched in 1989.
At the time of his most lucrative stroke of creative genius, in 1982, Johnson was an engineer at the Strategic Air Command in Omaha, Neb., working in his spare time on a new type of heat pump that would use water instead of Freon.
He hooked up a model of the pump to the bathroom sink in his home.
"I turned around and I was shooting this thing across the bathroom into the tub and the stream of water was so powerful that the curtains were swirling in the breeze it sent out," he said. "I thought, `This would make a great water gun."'
The Pneumatic Water Gun was what he dubbed the first prototype. He received the patent -- No. 4,591,071 -- for the squirt gun in 1986, but he decided not to manufacture the plastic gun himself after determining it would cost $200 per gun for the first 1,000.
Then in 1989, he met some executives with Larami Corp. at a toy fair. Two weeks later, he was sitting in the company's conference room with a model of the Super Soaker he had created out of a plastic Coke bottle, PVC pipe and Plexiglas.
"I pumped it up and fired it across the conference room," he recalled. "Ww," was the reaction from the suited executives. "From that point it was a done deal."
The Super Soaker, for which Johnson received a patent in 1988, was introduced into the market in 1990 with a pumped-up reservoir capable of firing a stream of water up to 50 feet.
Today, more than 250 million of the high-tech water weapons have been sold, according to Al Davis, Larami executive vice president.
"That's four guns to every kid in the United States," Davis said, noting that the plastic toys also found a surprise market among adults.
The giant water guns range the gamut from a $5 pocket-size version to the $50 CPS-3000, a plastic weapon with a 2-gallon backpack guaranteed to soak its target.
Johnson, a modest father of three, refused to disclose exactly how much his toy invention has earned him.
"I'm doing quite well," he said. "Put it like this, I could close this place down and go lay on the beach if I wanted to."
Written By Patricia J. Mays