This paper is written to introduce the third off-set strategy of the U.S. Armed Forces and to draw a few implications for South Korea. The U.S. initiated the first off-set strategy by the President Dwight Eisenhower, who tried to off-set the massive ground forces of the U.S.S.R. by developing dominant nuclear weapons in the name of "New Look" policy. The Second off-set strategy was pursued by then Defense Secretary Harold Brown in 1970s through the development of cutting-edge military technologies. This third off-set strategy became necessary in order to overcome the two challenges, which were the continuous reduction of defense budgets and the re-emergence of threats from big countries such as Russia and China. The U.S. Armed Forces has been trying to focus on the new technologies to deal with these two challenges simultaneously. The fields for technological innovation include unmanned operations, extended-range air operations, low-observable air operations, undersea warfare, complex systems engineering and integration. However, this off-set strategy has some risks. The U.S. may not succeed to develop the innovative technologies necessary. There is no guarantee that the new technologies are to provide the victory in the future war. It is not clear whether the third strategy is acquiring consensus among the U.S. Armed Forces, because the use of term has dramatically decreased since the replacement of the Secretary of Defense Chuck Hagel at the end of 2014. As implications for South Korea, the third off-set strategy may reduce the commitment of the U.S. extended deterrence or nuclear umbrella and result in the reduction of the U.S. troops in South Korea. The U.S. could demand the increase of self-sufficiency of the South Korean military. Therefore, South Korean Armed Forces should keep track of the status of the third off-set strategy of the U.S. forces, strengthen self-reliance in the defense of North Korean nuclear weapons and try to participate the U.S. third off-set strategy by developing several comparatively advantageous military technologies.