NSSIF is a UK government strategic investment fund for national security and defence that deploys venture-style capital into dual-use deep tech companies and also invests indirectly through venture capital funds. It backs early-stage UK startups developing strategically relevant technologies across defense, security, aerospace, space, AI, cybersecurity, computing, semiconductors, robotics, drones, telecommunications and manufacturing, and is relevant for founders seeking institutional capital plus government customer connections and strategic insight.