Pursuant to Section 101(a)(5)(A) of the Marine Mammal Protection Act (MMPA) (16 U.S.C. 1361 et seq. ), the National Marine Fisheries Service (NMFS), upon application from the U.S. Department of the Navy (including the U.S. Navy and the U.S. Marine Corps) and on behalf of the U.S. Coast Guard and U.S. Army, plans to propose regulations to govern the unintentional taking of marine mammals incidental to training and testing activities conducted in the Hawaii California Training and Testing (HCTT) Study Area in support of military readiness activities. The proposed regulations would set forth the permissible methods of taking; other means of effecting the least practicable adverse impact on the affected species or stocks and their habitats ( i.e. , mitigation); and, if applicable, on their availability for taking for subsistence uses; and requirements pertaining to the monitoring and reporting of such taking. Letters of Authorization (LOAs) issued under the regulations would authorize the take of marine mammals incidental to the specified activities for a 7-year period beginning December 2025. Three LOAs issued under the regulations would authorize the take of marine mammals incidental to the Navy’s specified training and testing activities, the Coast Guard’s training activities, and the Army’s training activities to be conducted within the HCTT Study Area. The HCTT Study Area includes areas in the north-central Pacific Ocean, from California west to Hawaii and the International Date Line, and including the Hawaii Range Complex, Southern California (SOCAL) Range Complex, Point Mugu Sea Range, and the Northern California (NOCAL) Range Complex. NMFS’ proposed rule, if issued, would authorize take of individuals of 42 marine mammal species by Level A and B harassment, and a small number by injury or mortality from vessel strikes and explosives.