Herbert G. "Mac" MacPherson (1911-1993) was an American nuclear engineer.
MacPherson's expertise on graphite made him a valuable consultant for the Manhattan Project. He co-developed a method to produce massive quantities of nearly boron-free graphite, a discovery important to the success of the nuclear reactors at Oak Ridge and Hanford. As Alvin Weinberg later noted, without his contributions, "the plutonium-producing reactors at Hanford would not have chain-reacted."
In 1956, MacPherson joined Oak Ridge National Laboratory, where he later served as deputy director. He also played a major role in developing the molten salt reactor, an experimental nuclear reactor, at Oak Ridge.