The following is the March 13, 2024, Congressional Research Service In Focus report, Navy TAGOS-25 Ocean Surveillance Shipbuilding Program: Background and Issues for Congress.
From the report
Introduction
The Navy in FY2022 procured the first of a planned class of seven new TAGOS-25 class ocean surveillance ships at a cost of $434.4 million. The Navy’s FY2024 budget submission showed that the ship’s estimated procurement cost had subsequently grown to $789.6 million—an increase of $355.2 million, or 81.8%. The Navy’s proposed FY2024 budget requested $355.2 million in additional cost-to-complete procurement funding to pay for this cost growth. Under the Navy’s FY2024 budget submission, the Navy wanted to procure the second TAGOS-25 class ship in FY2025.
Under the Navy’s FY2025 budget submission, the Navy is proposing to defer procurement of the second TAGOS-25 class ship from FY2025 to FY2026. The Navy’s proposed FY2025 shipbuilding budget requests no procurement funding for the TAGOS-25 program.
Meaning of TAGOS Designation
In the designation TAGOS (also written as T-AGOS), the T means the ships are operated by the Military Sealift Command (MSC); the A means they are auxiliary (i.e., support) ships; the G means they have a general or miscellaneous mission; and the OS means the mission is ocean surveillance.
TAGOS Ships in the Navy
TAGOS ships (Figure 1 and Figure 2) support Navy antisubmarine warfare (ASW) operations. As stated in the Navy’s FY2025 budget submission, TAGOS ships “gather underwater acoustical data to support the mission of the Integrated Undersea Surveillance System (IUSS) by providing a ship platform capable of theater anti-submarine acoustic passive and active surveillance.… The two current classes of [TAGOS] surveillance ships use Surveillance Towed-Array Sensor System (SURTASS) equipment to gather undersea acoustic data.” Figure 3 shows a simplified diagram of a TAGOS-25 ship with its SURTASS arrays.
Current TAGOS Ships
The Navy’s five aging TAGOS ships include four Victorious (TAGOS-19) class ships (TAGOS 19 through 22) that entered service in 1991-1993, and one Impeccable (TAGOS-23) class ship that entered service in 2000. As of the end of FY2023, all five were homeported at Yokohama, Japan. The ships use a Small Waterplane Area Twin Hull (SWATH) design, in which the ship’s upper part sits on two struts that extend down to a pair of submerged, submarine-like hulls (Figure 2). The struts have a narrow cross section at the waterline (i.e., they have a small waterplane area). The SWATH design has certain limitations, but it has features (including very good stability in high seas) that are useful for SURTASS operations.
Download the document here.
