DOD acquires new weapons for its warfighters through a management process known as the Defense Acquisition System. Chapter 1 contains GAO's 16th annual assessment of the Department of Defense's (DOD) $1.66 trillion portfolio of 86 major weapon systems acquisition programs. It examines changes in the portfolio since 2016, including DOD's progress implementing acquisition reforms. The Department of Defense (DOD) faces mounting challenges in protecting its weapon systems from increasingly sophisticated cyber threats. Chapter 2 addresses (1) factors that contribute to the current state of DOD weapon systems' cybersecurity, (2) vulnerabilities in weapons that are under development, and (3) steps DOD is taking to develop more cyber resilient weapon systems.