Aug. 16, 2024 Sentinel: The History of the DAF Modernizing the Backbone of America’s National Security The U.S. Air Force is replacing the 54-year-old LGM-30G Minuteman III ICBM weapon system with the LGM-35A Sentinel ICBM. Upgrading to Sentinel ICBMs ensures the land-based leg of America's Nuclear Triad remains safe, secure and effective.