Baltic Security Initiative Act This bill requires the Department of Defense (DOD) to carry out an initiative to deepen security cooperation with Estonia, Latvia, and Lithuania. The goals of this initiative include (1) achieving U.S. national security objectives by deterring Russian aggression; (2) enhancing regional planning and cooperation among these countries, particularly with respect to long-term regional capabilities such as long-range precision fire systems and integrated air and missile defense; and (3) improving these countries' cyber defenses. DOD must also submit to Congress a strategy for accomplishing these goals.