Indo-Pacific Deterrence Initiative This bill directs the Department of Defense (DOD) to establish the Indo-Pacific Deterrence Initiative. The bill also authorizes various related programs. The initiative shall seek to (1) enhance U.S. presence in the region by positioning U.S. capabilities to allow timely response to adversarial threats, (2) strengthen the capability of U.S. forces and regional allies and partners, and (3) meet objectives under the National Defense Strategy. The U.S. Indo-Pacific Command may carry out social media-related activities to counter misinformation and propaganda in the region. The bill also authorizes for FY2021 various activities and projects, including a permanent and persistent land-based air and missile defense system in Guam; a homeland defense radar in Hawaii; Missile Defense Agency activities in the region; intelligence, reconnaissance, and related capabilities for the U.S. Indo-Pacific Command; a Marine Unit Deployment Program and Marine Corps rotational presence in the region; Air Force and Navy unit pre-positioning for regional activities; DOD procurement of key munitions for the Indo-Pacific Command; military construction, land acquisition, and military family housing functions; a program to enhance communications capabilities with allies and partners in the region; and various training activities, such as joint training through the Combatant Commanders Exercise Engagement and Training Transformation Program.