America is not ready for a coordinated drone attack. Without investment in counter-drone technologies, we are susceptible to a 21st-century Pearl Harbor. The right moves would protect economic and national security in a new era in which speed, surprise, and scale dominate. It is essential that America leads the world in both drone innovation and security. Here are four actions from Matt Cronin, a16z senior national security advisor, that the US can take to close the gap in our defenses: