Since the Reggie secondary manufactured in the UK from British-owned materials was a copy of the US W-59, by implication, the W-59 thermonuclear weapon deployed in some Minuteman I ICBMs also used the fission-fusion-fission process.
Fault Tree Analysis (FTA) was originally developed in 1962 at Bell Laboratories by H.A. Watson, under a U.S. Air Force Ballistics Systems Division contract to evaluate the Minuteman I Intercontinental Ballistic Missile (ICBM) Launch Control System.