As a global leader in science, technology and military power, the United States has a profound influence on the global scientific landscape through its research funding strategies and priorities. This paper conducts topic mining and evolution analysis of the key science and technology funding projects of U.S. Department of Defense from 2015 to 2024 based on the BERTopic model. From the perspectives of topic distribution and dynamic topic evolution, it provides an empirical and systematic examination of the strategic layout and constituent factors of U.S. defense science and technology funding. The results show that the Department of Defense’s key science and technology funding projects cover 83 topics. While most topics exhibit relatively stable frequency changes over time, a small number demonstrate significant fluctuations or rapid growth, reflecting a key technology funding strategy that emphasizes “concentrated resource investment in core areas while broadly fostering emerging directions.” Overall, the U.S. Department of Defense have achieved the advancement of basic and applied research in the process of promoting science and technology, thereby constructing a frontier technology ecosystem oriented toward national security.