Sunday, November 29, 2015


One of the vital but relatively unknown vessels of the Navy is the T-AGOS ocean surveillance ships.  The Navy operates a small fleet of these vessels under the Military Sealift Command.  This post offers a brief look at these vessels and their function.

As you might imagine, getting detailed information on the functionality of these ships is difficult.  The vessels are broadly tasked with surveillance of submarines.  Presumably this includes both tracking of submarines and development of detailed acoustic profiles of submarine classes and specific submarines.  Their primary “weapon” is the SURTASS surveillance towed array sensor system which is intended to monitor submarines at very long ranges. 

Additional functions include oceanographic and hydrographic data collection.

SURTASS is the mobile version of the well known SOSUS system.  In its baseline configuration, the array was passive only but now includes a vertical array active low frequency (LFA) source.  This allows operation in a bistatic mode.  USS Impeccable began operating the LFA in 2004.  Smaller versions of the LFA have been developed for the Victorious class vessels. Other versions of SURTASS are being developed for enhanced shallow water submarine detection.

The horizontal array is 4900 ft long and is towed at a depth of 500-1500 ft.

Ships and Characteristics
The Navy currently operates four T-AGOS ships of two classes.  The three-ship Victorious class was begun in 1986 and the one-ship Impeccable class was started in 1993.  Additional ships were planned in the Impeccable class but were cancelled for budget reasons.

The ships are built with SWATH (Small Waterplane Area Twin Hull) hulls for stability at low speed and in heavy weather.

The current list of active T-AGOS vessels is:

Victorious T-AGOS-19
Able T-AGOS-20
Effective T-AGOS-21
Loyal T-AGOS-22
Impeccable T-AGOS-23

Here are a few physical characteristics for the Victorious class.  The Impeccable class is similar, though larger.

Length:                       234 – 281 ft
Displacement:           3400 – 5400 tons
Speed:                       10 – 13 kts;  3 kts when towing
Crew:                          20 mariners, 5 techs, and up to 15 Navy crew

USS Impeccable

Impeccable Incident

There is a demonstrable and common sense need to provide protection for these ships when they operate near unfriendly countries.  Impeccable was invoved in a famous incident of harassment by Chinese vessels in 2009 that illustrates the need for protection.  From a Naval War College report comes this summary of the incident (1).

“[Impeccable] … was engaged in lawful military activities in China’s claimed EEZ. On 8 March 2009, five PRC vessels—a navy intelligence ship, a government fisheries-patrol vessel, a state oceanographic patrol vessel, and two small fishing trawlers—surrounded and harassed Impeccable approximately seventy-five miles south of Hainan Island in the South China Sea. The fishing trawlers maneuvered within twenty-five feet of Impeccable and then intentionally stopped in front of it, forcing Impeccable to take emergency action to avoid a collision. The U.S. government protested the PRC’s actions as reckless, unprofessional, and unlawful. China responded that Impeccable’s presence in China’s claimed EEZ had been in violation of Chinese domestic law and international law. Impeccable returned to the area the next day under escort of a guided-missile destroyer, the USS Chung-Hoon (DDG 93).”

Note that Impeccable did not have effective protection during the incident.  Failure to provide protection is a recipe for disaster.  You’ll recall the Chinese forcedown and subsequent seizure and looting of the EP-3 aircraft some years back.  Without ready protection, we run the risk of losing a valuable and highly secret vessel.

The Navy continues to search for a mission the LCS can be effective at.  Adapting a LCS to the T-AGOS mission would be a possibility.  With at least a minimal level of self-protection as well as some useful speed, the LCS-AGOS could operate with a degree of defensive capability that the T-AGOS does not possess.  Of course, the LCS is inherently endurance-challenged but modifications ought to be possible to greatly increase the range and endurance.  This is not a perfect option but might be a way to get more use out of an otherwise fairly useless platform.

In summary, the T-AGOS vessels provide a very valuable function in the Navy’s subsurface warfare effort and, though less glamorous, deserve increased attention, upgrades, and protection.  All in all, an interesting class of ship!


  1. There are at least four cases where unescorted intelligence assets where attacked resulting in crew deaths or the surrender of the intelligence asset.

    USS Liberty
    USS Pueblo
    1969 EC-121 Shoot down
    Hainan island incident

    1. Quite right. Thanks. I was attempting to highlight only the incident involving this class of ship but the concept of protecting intelligence and surveillance units applies to all platforms.

    2. ?? Given that many why don't we protect them? Seriously? Anti piracy work or 'presence' missions are more important?

    3. It's quite odd that our most secretive and valuable assets, flying/sailing near unfriendly areas receive no ready protection. There have been numerous reports of unsafe harassment of aircraft. We leave these assets hanging out on their own. Puzzling, especially after the various incidents over the years. It's not like it's a surprise when it happens, anymore.

  2. Sounds about perfect. Bit over kill.

    One wonders how long and LCS can sustain its full speed as the escort roll could be done at a distance along with a "patrol" roll ?

    Otherwise its a hellishly expensive asset for the job.

    1. Not a perfect fit for the LCS but I, and the Navy, continue to cast about for some useful role for the LCS. Still looking!

      Aside to Ben: Tomorrow.

    2. This would be another job better done by the HI patrol frigate.

      In my town we have an old SURTASS ship. I've been on her. They are pretty nice actually.

      Its the old T/AGOS Persistent.

    3. Lucky you! I'd love to see one.

    4. They are pretty nice. All the TAS stuff has been pulled off as its a great lakes maritime academy ship now. One of the guys giving the tour was ex Navy. I did chuckle when I pointed out how nice the crew accomodations were. "Oh yeah. When I was on a 'Burke I had (X) inches. These kids have entire rooms..."

  3. You ignored its key advantage, diesel electric engines, which allow it to cruise slow and quiet to find subs. They have no weapons so they are not warships and cannot be attacked when they "accidentally" go off course several miles within the 12-mile limit while doing "ocean research".

    But .50 cals were mounted on the Pueblo just before she sailed, and her captain "followed orders" and refused to leave N. Korea waters for over a hour when confronted by NK boats, so it was boarded. All went according to plan, but the reason for this plan no one knows for sure.

  4. I wonder if they are set up to run silently like the Spruances.

    1. They do reportedly have quieting features though I've never heard any details.


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