Explanations of Japanese technological modernization from the late nineteenth to the mid-twentieth century have increasingly focused on domestic capabilities as opposed to the traditional emphasis on knowledge transfers from the West. Yet, the literature is mostly qualitative and it lacks a comparative context. This article presents quantitative metrics derived from patent data covering Japan, the United States, Britain and Germany and it also exploits non-patent based sources. The evidence shows that Japanese domestic inventive activity exhibited a pattern of rapid modernization to the technology frontier in terms of its level, sectoral distribution and quality. Domestic capabilities were much stronger than is often supposed in accounts that stress the prevalence of Western technology diffusion. A long run expansion in indigenous development set a favorable foundation for the economic growth miracle Japan experienced after the Second World War.