Pursuant to Section 101(a)(5)(A) of the Marine Mammal Protection Act (16 U.S.C. 1361 et seq.) (MMPA), the National Marine Fisheries Service (NMFS), upon application from the U.S. Navy (Navy), will propose MMPA regulations to govern the unintentional taking of marine mammals by harassment, and a small number of mortalities, incidental to military readiness training and testing activities to be conducted in the Hawaii-Southern California Training and Testing (HSTT) Study Area. On July 10, 2020, NMFS issued seven-year regulations governing the taking of marine mammals incidental to Navy training and testing activities conducted in the HSTT Study Area (85 FR 41780), including three takes of large whales by serious injury or mortality by vessel strike. In 2021, two separate U.S. Navy vessels struck unidentified large whales on two separate occasions, one whale in June 2021 and one whale in July 2021. The Navy has reanalyzed the potential for vessel strike in the HSTT Study Area and has requested that NMFS authorize two additional takes of large whales by serious injury or mortality by vessel strike for the remainder of the regulatory period (through December 20, 2025). The proposed regulations would revise the existing HSTT regulations and associated Letters of Authorization (LOAs) such that they would cover additional incidental take in the form of serious injury or mortality by vessel strike. The Navy did not request changes to their currently authorized specified activities, mitigation measures, monitoring, or reporting. 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. LOAs issued under the regulations would authorize the take of marine mammals incidental to the Navy’s specified training and testing activities to be conducted within the HSTT Study Area over the remainder of the regulatory period.