PASADENA, Calif. -- Robert F. Christy, a former California Institute of Technology professor who helped design the trigger mechanism for the atomic bombs used in World War II, died Wednesday. He was 96.

Christy died of natural causes at his home in Pasadena, surrounded by his family, according to Caltech spokeswoman Deborah Williams-Hedges.

Christy was one of the early recruits to the Manhattan Project at Los Alamos Laboratory, a U.S. government research project to develop atomic weapons during the war. He was hand-picked to join by his University of California, Berkeley, professor J. Robert Oppenheimer, with whom Christy studied quantum mechanics.

The Canadian native devised what came to be known as the Christy bomb or Christy gadget, a plutonium implosion device.

Before the Manhattan Project began, Christy researched with the era's leading physicists, including Italian Enrico Fermi and Hungarian Eugene Wigner.

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"What I was told was that they were trying to make a chain reaction. And the purpose of the chain reaction -- well, it might be to drive submarines, or whatever. I was not told about bombs at the time," Christy said in a 1994 interview.

When the first bomb was tested at Los Alamos, Christy said everyone was pleased to have succeeded in the experiment, but a month later, when the atomic bomb was dropped on Hiroshima, it was a very sobering experience.

"There had been bombs dropped on cities," he said. "There had been firestorms, and so forth. I believe people nowadays don't realize that in war your objective is to beat the enemy. And unfortunately, mostly that involves killing a lot of the enemy to do that."

At Caltech, Christy taught theoretical physics, nuclear physics and astrophysics and went on to serve as faculty chair, vice president and provost and acting president.