The paper presents a previously unpublished index of the total British output of munitions, 1942-5. The index was produced in the Ministry of Production's Programmes Division under E.A.G. (now Professor Sir Austin) Robinson in both weekly and monthly versions. The Robinson index was used mainly for purposes of short run management of munitions production and manpower budgets. For today's more long run historical purposes the index can be revised and extended back to 1939 on a quarterly basis. The revised index shows a fourfold increase in British munitions output in the first 18 months of the war; by the 1944 peak, munitions output was running at more than six times the October-December 1939 rate. The level and dynamic of British munitions output estimated in this way can also be compared with the performance of similar indicators of munitions output in World War II in other countries.