The U.S. Navy halted development of an anti-torpedo defense system for its ships last year due to poor performance, including unreliable sensors and interceptor torpedoes, and will remove the prototype systems from five carriers over the next four years. This comes at a time when the service routinely sounds the alarm about growing submarine threats, especially to high-value ships, from potential “great power competitors,” such as Russia and China.
The latest annual report from the Pentagon’s Office of the Director of Test and Evaluation, or DOT&E, revealed the Navy’s decision to suspend work on what it officially calls the Anti-Torpedo Torpedo Defense System (ATTDS) in September 2018. DOT&E issues these reports to provide a public summary of significant testing developments regarding major U.S. military programs in the preceding fiscal year.
At present, three of the Navy’s Nimitz-class aircraft carriers – USS George H.W. Bush, USS Harry S. Truman, and USS Nimitz – have prototype engineering and development models of the ATTDS installed. Bush was the first to receive the ATTDS in 2013. Two more Nimitz class carriers, the USS Dwight D. Eisenhower and USS Theodore Roosevelt, initially had earlier interim roll-on/roll-off versions of the system, but the Navy eventually added full prototypes to those ships.
The basic components of the ATTDS on all five carriers are the same. It consists of the Torpedo Warning System (TWS) and the Countermeasure Anti-Torpedo (CAT).
The TWS includes a towed acoustic sensor that trails behind the ship to detect potential threats, classify them, and provide targeting information for the CAT. The CAT is a torpedo-like “hard-kill” interceptor that homes in on the torpedo and destroys it either by physically smashing into it or with its own explosive warhead. You can read more about the system and how the Navy expected it to work here.
The problem, according to DOT&E, is that after more than five years in development, the ATTDS's demonstrated capabilities were improving, but not fast enough. The system’s performance in testing and other evaluations, including during operational deployments on Bush, Eisenhower, and Nimitz in the 2017 Fiscal Year, was limited.
“TWS demonstrated some capability to detect incoming torpedoes,” DOT&E’s report for the 2018 Fiscal Year explained. “The significance and effect of false target alerts on TWS capability are unknown.”
“CAT demonstrated some capability to defeat an incoming torpedo,” the annual review continued. “CAT has uncertain reliability. The lethality of CAT is untested.”
In short, the two major components of the torpedo defense system have shown, in principle, that they might be able to destroy an incoming threat, but they’re not reliable enough to accurately evaluate those capabilities. The latest DOT&E report is otherwise light on specific details.
However, DOT&E reviews from previous years do shine some additional light on significant ongoing issues. For one, the system reportedly suffers a high rate of false alarms when large numbers of other ships are present. This could suggest the TWS might have difficulty spotting an actual threat amidst other friendly ships, neutral vessels a hostile submarine might use to hide its approach, or anything else creating acoustic signatures during an actual combat scenario.
The active acoustic sensor component of the system, which might’ve helped mitigate that with its ability to actively search for targets, was still in testing at the time the Navy halted work in 2018. In every instance that a carrier had deployed with the ATTDS installed, the TWS was capable of passive detection only. DOT&E’s report for the 2017 Fiscal Year said that crews onboard Bush, Eisenhower, and Nimitz had rarely bothered to roll out the TWS array during their cruises and therefore collected little information on how it might work under real-world conditions.
DOT&E also criticized the Navy’s use of highly scripted tests to evaluate the CAT’s performance, as well as how relevant the surrogate torpedo targets actually were. The service’s existing training targets are modified American designs and are not meant to reflect any foreign torpedo’s specific capabilities. As such, while the testing met the Navy’s requirements, DOT&E said it was impossible to gauge whether the data was representative of how the anti-torpedo interceptor would perform against a real threat.
The ATTDS was supposed to be part of the larger Surface Ship Torpedo Defense (SSTD) system, which also includes the AN/SLQ-25 Nixie and the Mk 2 Acoustic Device Countermeasure (ADC), both of which are in widespread Navy service already. The Nixie is a towed decoy meant to lure enemy homing torpedoes. The ADC is a standoff system that gets launched from Navy ships and then settles at a predetermined depth pumping out acoustic noise to attract homing torpedoes.
The complete arrangement was supposed to provide important close-in protection against underwater threats for Navy carriers and other high-value ships, such as amphibious assault ships. The added protection ATTDS is supposed to offer reflects the very real and growing threat of advanced submarines, including steadily harder to detect diesel-electric types with air-independent propulsions (AIP) systems. China and Russia are both looking to expand the size and capabilities of their submarine fleets and many of their new, non-nuclear submarine designs are available for export, increasing the chance that these potential threats will proliferate.
This is to say nothing of increasingly capable Chinese and Russian torpedoes, many of which are also available on the export market. The latest variants and derivatives of Russia’s Type 53 family have ranges in excess of 12 miles, have features to defeat acoustic countermeasures, and zig-zag in the terminal phase of their attack to make them particularly hard to evade or intercept.
Though its general configuration is reverse engineered from the U.S. Mk 48 torpedo, China’s Yu-6 reportedly has some similar capabilities to the Type 53. In 2012, the Chinese People’s Liberation Army Navy (PLAN) introduced the Yu-9, which is a quieter, electrically-powered version of the Yu-6 that is more difficult to detect.
However, the most recent report from DOT&E does not offer any recommendations for how the Navy might proceed, strongly implying that the ATTDS program might end up heavily restructured or canceled entirely. In 2017, the Navy pushed back the planned date for reaching initial operational capability with the system from 2018 to 2022.
As of 2016, the service had hoped all of its carriers and other high-value ships would have the new anti-torpedo defenses by the end of 2035. Now it will remove all of the ATTDS components from the five carriers with the system by the end of 2023.
Still, it seems hard to believe that the Navy wouldn’t at least try to squeeze some capability out of the system. The service has received more than $760 million in funding for the continued development of the entire SSTD, including almost $85 million in the ATTDS in the 2017 and 2018 Fiscal Year defense budgets alone.
As already noted, there is certainly a continuing need for improved anti-torpedo defenses that only looks set to grow in urgency the coming years, as well. Whether ATTDS, or a revamped version of the system, ultimately provides the capability or not, the Navy’s expensive carriers and other major surface ships are still in desperate need of a more robust array of defenses against enemy submarines.
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