Orange Herald was a fusion boosted British fission nuclear weapon, comprising a U-235 primary surrounded by lithium deuteride. 'Herald' was suitable for mounting on a missile, utilizing 117 kg of U-235. However, Britain's annual production of U-235 was only 120 kg at this time, which would have made such weapons rare and very expensive. Two versions were designed - an "Orange Herald Large" with an overall diameter of 39 inches (1.0 m), and an "Orange Herald Small" with overall diameter of 30 inches (0.75 m). Orange Herald was the first British nuclear device to use an external neutron source.