This paper aims to examine the difference between US and European manufacturing before and during the World War II, focusing on the key technology in the metal-working sector: machine tools. We present a new data set covering the installed capacity of metal-working tools in the United States and Germany for the period 1930-1945. The existing literature is heavily dependent on assumptions about the different type of machine tools in use on either side of the Atlantic. So far, systematic comparison has been limited to case studies. This is the first attempt to quantify the differences in this key technology for the entirety of metal-working in both economies. The enormous detail of the statistical sources we have uncovered allows us to combine aggregation and a degree of specificity, which exceeds that of any previous case study. In the German case, the original data is divided into well over a hundred sub-categories. For comparative purposes, we have identified 19 major classes of machines, which aggregate over 50 sub-categories. Our results suggest the need for a far more nuanced understanding of metal-working than the dichotomous picture of American mass manufacture, reliant on special-purpose tools, and European craft manufacturing employing general-purpose machinery. For 1930, we find a remarkable similarity in machine to worker ratios between Germany and the United States. There are differences in certain key areas. However, the US stock of metal-working tools is not yet distinguished by a clear commitment to mass production technology. For the period after 1935, until the early 1940s, our data suggest a remarkable degree of convergence. The American stock stagnated. In some areas, there was disinvestment. And the average age of machinery rose dramatically. By contrast, Germany entered a period of rapid catch-up, which appears to have continued into the early years of the war. By 1940, German metal-working came close to matching its American counterpart in terms of the number of workers employed and the quantity and types of machines installed. German machines were, on average, far younger. This process of catching-up, however, was dramatically reversed during World War II. Over a period of no more than four years the American stock expanded by over eighty percent and growth was markedly concentrated in key categories of mass production equipment. It appears that it was only in this period that mass production machinery came to truly dominate US metal-working. German investment, albeit moving in the same direction, failed to match the new intensity of American commitment to mass production in some key machinery classes