Navy TAGOS-25 Ocean Surveillance Shipbuilding Program: Background and Issues for Congress

Navy TAGOS-25 Ocean Surveillance Shipbuilding Program: Background and Issues for Congress

Navy TAGOS-25 Ocean Surveillance Shipbuilding Program: Background and Issues for Congress

Updated December 4, 2025 (IF11838)

Introduction

The Navy in FY2022 procured the first of a planned class of seven new TAGOS-25 class ocean surveillance ships. The Navy's proposed FY2026 budget requests $612.2 million for the procurement of the second ship in the class.

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 FY2026 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. T-AGOS ships are operated by Military Sealift Command to support the anti-submarine warfare mission of the commanders of the Atlantic and Pacific Fleets. The two current classes of surveillance ships use Surveillance Towed-Array Sensor System (SURTASS) equipment to gather undersea acoustic data. The ships also carry electronic equipment to process and transmit that data via satellite to shore stations for evaluation." 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 19-22) that entered service in 1991-1993, and one Impeccable (TAGOS-23) class ship that entered service in 2000. As of the end of FY2024, 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., a small waterplane area). The SWATH design has features (including very good stability in high seas) that are useful for SURTASS operations.

TAGOS-25 Program

Class Name

On January 10, 2025, the Navy announced that TAGOS-25 class ships would be called the Explorer class, "in honor of those who made discoveries under sea, on land, and in the skies above," and that the first two ships in the class (TAGOS-25 and TAGOS-26) would be named Don Walsh and Victor Vescovo, respectively.

Figure 1. USNS Impeccable (TAGOS-23)

Source: U.S. Navy photograph accompanying "Ocean Surveillance Ships," Military Sealift Command, accessed May 25, 2021.

Figure 2. USNS Effective (TAGOS-21) in Dry Dock

Source: U.S. Navy photograph 070913-N-2638R-004, posted at Wikimedia Commons, accessed May 25, 2021.

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, and the Navy's FY2026 budget submission states that it is scheduled to be delivered in July 2031. The Navy's TAGOS-25 design (Figure 4) is larger and faster than the in-service TAGOS ships, with a full load displacement of 8,901 tons and a maximum speed of 20 knots, compared to 3,384 and 5,370 tons, and 10 and 13 knots for the TAGOS-19 and TAGOS-23 designs, respectively.

Figure 3. TAGOS Ship with SURTASS Arrays

Source: Detail from slide 13, entitled "TAGOS(X) Concept of Operations (CONOPS)," in Industry Day briefing for TAGOS(X) program, June 26, 2019, accessed May 26, 2021, at GovTribe.com.

Figure 4. Notional Navy Design for TAGOS-25

Source: U.S. Navy rendering shown in GAO report 25-107569.

Builder

On May 18, 2023, the Navy announced that it had awarded Austal USA, a shipyard in Mobile, AL, a fixed-price incentive (firm target) and firm-fixed-price contract for detail design of the TAGOS-25 class. The contract includes options for the detail design and construction of up to seven TAGOS-25s plus associated work.

Cost, Schedule, Technical Risk

A January 2025 Congressional Budget Office (CBO) report on the Navy's FY2025 30-year shipbuilding plan estimated the cost of a nine-ship (rather than seven-ship) TAGOS-25 program, stating, "CBO estimates that the 9 T-AGOS(X) ships would cost an average of $900 million each—twice the Navy's estimate of an average of $450 million per ship."

A June 2025 Government Accountability Office (GAO) report (GAO report 25-107569) states,

Since the program exercised the lead ship construction option in May 2024, shortages in ship design resources and lags in receiving vendor furnished information delayed contractor progress on the design. The shipbuilder is working to develop a new schedule, which the program estimated would be available in mid-2025. The program has yet to set a date for the start of lead ship construction. Officials stated that, as of October 2024, the functional design was only 12 percent complete, far below the contract requirement that it be 100 percent complete to start construction….

… A SWATH ship that meets the program's requirements for speed, seakeeping, and endurance has never been built, making the design a significant risk for the program…. [Program officials] noted that keeping the [ship's] weight [i.e., displacement] in an acceptable margin imposes risk to schedule and cost, which would be exacerbated by beginning construction work prior to completing the functional design….

… the [Navy's] 3D model requirements [for developing the ship's design] fall short of [commercial shipbuilding] leading practices…. Our previous work has shown that setting design expectations that are below leading practices contributes significant risk to cost and schedule….

… According to the [TAGOS-25] program [office], its use of a 3D product model is consistent with modern commercial and naval shipbuilding standards and best practices. However, it is not using a digital twin or digital thread, which could ensure different systems and subsystems work together to maximize modularity and the efficiency of design and construction of follow-on ships….

Austal USA is currently executing work for 12 new construction programs for Navy and Coast Guard ships, up from two programs in 2021. Resource and workforce demand from these other programs could impose cost and schedule risks for the T-AGOS 25 program. (Page 152)

FY2026 Funding

The Navy's proposed FY2026 budget requests $612.2 million in procurement funding for the procurement of the second ship in the class.