The following is the Congressional Research Service May 18, 2023 In Focus report, Navy TAGOS-25 Ocean Surveillance Shipbuilding Program: Background and Issues for Congress.
From the report
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 shows that the ship’s estimated procurement cost has since grown to $789.6 million—an increase of $355.2 million, or 81.8%. The Navy’s proposed FY2024 budget requests $355.2 million in additional cost-to-complete procurement funding to pay for this cost growth. The Navy wants to procure the second TAGOS-25 class ship in FY2025.
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. The TAGOS-25 program was previously known as the TAGOS(X) program, with the (X) meaning that the precise design for the ship had not yet been determined. Some Navy budget documents may continue to refer to the program that way.
TAGOS Ships in the Navy
TAGOS ships support Navy antisubmarine warfare (ASW) operations. As stated in the Navy’s FY2024 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 FY2021, 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 . 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.
Quantity, Schedule, and Design
The Navy wants to procure seven TAGOS-25 class ships as replacements for its five in-service TAGOS ships. The first TAGOS-25 class ship was procured in FY2022. The Navy wants to procure the second through fifth ships in the class in FY2025-FY2028 at a rate of one ship per year. The Navy’s notional design for the TAGOS-25 class employs a SWATH design that would be larger and faster than the in-service TAGOS ships.
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