Welcome to the United States (U.S.) Department of the Navy’s (Navy) Surveillance Towed Array Sensor System (SURTASS) Low Frequency Active (LFA) Active Ship Training and Testing in the Western North Pacific and Indian Oceans environmental planning website.

This website is an online resource for information on the preparation of the Supplemental Environmental Impact Statement/Overseas Environmental Impact Statement (SEIS/OEIS) to assess potential environmental effects associated with the Proposed Action to conduct at-sea military readiness activities within the SURTASS LFA Ship Training and Testing Study Area (referred to as the “Study Area”). To meet training and testing requirements of the Navy, as the lead agency, along with the National Marine Fisheries Service (NMFS) as a cooperating agency, the Navy has prepared a Draft SEIS/OEIS, which is currently available for public review and comment through July 28, 2025. The Draft SEIS/OEIS includes an analysis of the potential environmental effects associated with the testing and training of the SURTASS LFA sonar system in the non-Artic areas of the western and central North Pacific and eastern Indian Oceans (Study Area) from 2026 through 2033.

The development of the SEIS/OEIS will help the Navy meet their environmental compliance requirements, while ensuring military readiness by:

• Supporting training and testing requirements;
• Increasing LFA sonar training hours to ensure the Navy remains proficient in the use of SURTASS LFA sonar in support of the Navy’s mission;
• Conducting at-sea sonar testing of up to one new SURTASS LFA sonar vessel per year;
• Updating environmental analyses using the best available science and analytical methods; and
• Supporting Marine Mammal Protection Act (MMPA) and Endangered Species Act consultations for the reissuance of federal regulatory permits and authorizations within the Study Area.

The Draft SEIS/OEIS includes an analysis of utilizing SURTASS LFA sonar onboard U.S. Navy surveillance ships. Proposed activities for this Draft SEIS/OEIS are similar to those analyzed in the 2019 SURTASS SEIS/Supplemental OEIS (SOEIS). However, this Draft SEIS/OEIS uses new information, including an updated acoustic analysis, updated marine mammal density data, and evolving and emergent best available science. Training and testing activities would employ mitigation measures intended to reduce or avoid adverse effects on marine species. The Draft SEIS/OEIS supplements the 2019 SEIS/SOEIS.

The Pacific SURTASS LFA Study Area (see Figure 1) consists of a large portion of the non-arctic western North Pacific Ocean and eastern Indian Ocean. The geographic scope analyzed in this document remains the same as that analyzed in the 2019 SEIS/SOEIS.

Figure 1.   Study Area for the Pacific SURTASS LFA Sonar Systems in the non-Arctic areas of the Western and Central North Pacific and Eastern Indian Ocean

The Navy is seeking the issuance of regulatory permits and authorization under the MMPA and the Endangered Species Act associated with proposed training and testing activities to be conducted in the Study Area beginning in 2026. NMFS will consider the potential effects of the Proposed Action on the marine environment pursuant to its authority under the MMPA, and to make a determination whether to issue an Initial Take Authorization and Letter of Authorization, including any conditions necessary to meet the statutory mandates of the MMPA.