William J. Thaler

William J. Thaler, Ph.D. (born December 4, 1925 – died June 5, 2005) was an American experimental physicist. Working for the Office of Naval Research (ONR) at the Naval Research Laboratory in the 1950s, Thaler developed an early warning system to detect the launching of ballistic missiles using high frequency radio waves bounced between the Earth's surface and the ionosphere, part of the upper atmosphere.

Monitoring the disruption of the returning radio waves, called back-scatter, allowed for the long distance detection of rocket launchings and nuclear tests. Based in the Washington D.C. area, the experimental monitoring systems, termed "over-the-horizon radar", were able to pick up radio disruptions from nuclear tests held in Nevada and were later successful in tracking a Polaris missile fired from Cape Canaveral.