In 1952, Britain committed itself to the development of a thermonuclear weapon. Kronberger's work on the separation of lithium isotopes was essential to the construction of the first warheads, which were tested at Christmas Island in 1957. A series of promotions within the UKAEA followed; he became Scientist in Chief of the Reactor Group in 1962 and the Member for Reactor Development of the UKAEA in 1969. Some of his work remains classified to this day, but there are many tributes to his inspiring leadership. He became involved with the promotion of peaceful uses of atomic energy and was a member of the Scientific Advisory Committee of the International Atomic Energy Agency. He contributed to feasibility studies on desalination of sea water and lectured on hydrostatic extrusion.