Abstract In early 1943 the Economic Warfare Division of the American Embassy in London started to analyze markings and serial numbers obtained from captured German equipment in order to obtain estimates of German war production and strength. This report is the story of the development of this technique in terms of the problems which arose and the ways in which they were solved. Various kinds of captured enemy equipment were studied by this technique. The first product to be so analyzed was tires, and after this tanks, trucks, guns, flying bombs, and rockets were studied. Aircraft markings were not studied by the Economic Warfare Division, since, by previous agreement, the British Air Ministry bore the responsibility for all estimates on aircraft production. The uses of the intelligence derived from the markings were varied. At times it helped decide the target systems of the air forces; on other occasions it gave indications of German strength in weapons such as tanks and rockets. After the war official statistics on German war production became available, so that it is now possible to evaluate the accuracy of the estimates which were made. Part II presents a summary scatter diagram of the estimates and official data along with a more detailed treatment of certain estimates.