The development of submicrosecond pulsed power in the U.K. and USA between 1960 and 1970 is described. Novel short-pulse (tens of nanoseconds) X-ray tubes driven by stacked solid dielectric striplines were devised at the Atomic Weapons Research Establishment, Aldermaston, U.K. for radiography. The importance of nuclear weapons effects simulation then motivated a very rapid development of new types of pulse generator in the USA to drive scaled-up tubes of this type. Prominent among these pulse generators were the Marx-driven liquid dielectric pulse lines that form the basis of many present-day pulsed power generators.