Delays And Cost Challenges Beset Airborne ASW

The U.S. Navy’s Boeing P-8A Poseidon maritime patrol and antisubmarine warfare (ASW) aircraft made the headlines in March when aircraft of patrol squadron VP-16, deployed to Kadena AB in Okinawa, supported the search for the vanished Malaysia Airlines Flight 370. But although the P-8A is the largest and most costly aircraft ever built for ASW, its ability to detect submarines at long range is inferior to that of the P-3C Orion, which it is intended to replace.

Meanwhile, France has had to accept a second reduction in its future ASW aircraft fleet. It had hoped to modernize 18 of its 22 Dassault ATL2 long-range patrol aircraft, but has had to settle for 15. The U.K., meanwhile, has yet to produce a plan to reinstate its once world-class airborne ASW capability, which disappeared when the Nimrod MR.2 and its intended successor the MRA4, were found not to comply with airworthiness standards.

But ASW is becoming much more challenging. The reason for the U.S. Navy’s capability gap is that the P-8A is the intended platform for a new sonar technology, required to handle submarine targets that have become much more elusive since the end of the Cold War. The Navy’s plan for some years has been to develop the P-8A airframe and above-water sensors, weapons and processors before integrating the sonobuoys and software that support Multistatic Active Coherent (MAC) acoustics in Increment 2 of the program, which is due to start flight tests late this year.

MAC is still in its early test stages (flying on P-3s) and has been demonstrated only in “benign” environments, according to the fiscal 2013 report from the Pentagon’s director of operational test and evaluation (DOT&E). Initial testing in 2013 “revealed unexpected performance shortfalls that are still being investigated,” the report stated, predicting that tests “to understand the effects different threat types and environments have on performance” would continue through 2019.

The time taken to field MAC is an example of what some observers see as disarray in the development of ASW in the U.S. “On ASW, the Navy’s in trouble,” says Norman Polmar, naval author, historian and consultant. “The Navy spent 45-55 years figuring out how to counter Soviet subs in the deep blue Atlantic and the threat now is a Venezuelan or Korean or Chinese submarine in relatively shallow waters.”

A multipolar world and the shift to a littoral strategy – absent a major blue-water mission comparable to the defense of Atlantic sea lanes – mean that diesel-electric submarines (SSKs) with air-independent propulsion (AIP) systems are now the leading threat. SSKs are growing in size and range, and AIP mitigates their principal vulnerability: an inability to go very far, or fast, without surfacing or snorkeling on noisy diesel power to recharge their batteries.

Polmar adds: “Our submarines rarely operate against nonnuclear subs, which is what the threat is. We periodically have South American submarines come up to Norfolk [Va.] or San Diego for exercises. Those are usually carefully scripted. We don’t want any problems or collisions. By the same token, we did borrow a Swedish AIP sub – the Gotland, which was homeported in San Diego in 2005-07. The Swedes told me they won in every exercise against our carrier group. Of course, we don’t talk about that.”

Internal politics play a role. The U.S. submarine sailors’ mantra has long been that the best ASW weapon is another submarine. The navy has not laid down an ASW-dedicated surface ship in almost 30 years; this role has been assigned to the multimission Littoral Combat Ship (LCS). (By contrast, the cash-strapped Royal Navy has designed the new Type 26 as a quiet ASW platform.) Reductions in LCS numbers mean fewer ASW-optimized Sikorsky MH-60R Romeo helicopters.

U.S. airborne ASW draws on Anglo-U.S. cooperation. The primary sensor for the MH-60R, the AQS-22 airborne low-frequency sonar, is a Raytheon-built version of a Thales design. The new MAC acoustic system uses a U.K.-developed sonobuoy, and was originally planned for its first operational use on the Royal Air Force’s canceled Nimrod MRA4. The Boeing-developed tactical control system on the MRA4 is closely related to the P-8A system. Under a 2007 contract, Ultra installed a MAC system on a Nimrod MR.2 and carried out an operational demonstration against real SSK targets, claiming “huge ASW performance gains.”

A key element of MAC is the U.K.’s Erapsco SSQ-125 sonobuoy – a joint venture of Ultra and Sparton – that can generate low-frequency coherent tones which can propagate for long distances. The older improved extended-echo-ranging system outfitted on the P-3 uses explosive charges to generate noise. Echoes can be detected by multiple receiver sonobuoys (hence “multistatic”).

MAC has several advantages. Unlike a monostatic active sonar, the submarine cannot turn end-on to the source to minimize the echo, because the receivers will detect echoes from its side. The signal is coherent (a tone or chord rather than noise), so it is possible for receivers to detect a Doppler shift and estimate the target’s speed and heading. MAC offers much greater range against a quiet SSK than a passive system. Both the source and receiver buoys can be fitted with GPS receivers for more accurate targeting.

The U.S. Navy plans to take advantage of MAC’s accuracy, plus the P-8A’s large sonobuoy load, to change the way that it conducts airborne ASW. Techniques for tracking sonobuoys accurately from high altitude, along with wing-kit-fitted torpedoes – Boeing received a contract for a test batch in April 2013 – combine with MAC to allow the P-8A to remain at high altitude and cover a much larger area. High-altitude ASW is important to the P-8A because the Boeing 737-based aircraft is less efficient at low altitude than the propeller-driven P-3. This was one reason for the omission of a magnetic anomaly detector (MAD) system from the U.S. Navy aircraft (although India’s P-8Is retain it): MAD requires low-altitude maneuvering to localize the target. Boeing is proposing an air-launched unmanned air vehicle, recoverable on land or on ship, to carry a MAD sensor.

Another ASW innovation, of U.S. origin, has had a long road to adoption. The automatic radar periscope detection and discrimination (Arpdd) project began at Johns Hopkins Applied Physics Laboratory in 1993. Arpdd uses very high scan rates and high-speed processing to pinpoint small objects out of sea clutter and discriminate between floating and slow-moving targets. The initial goal was to field Arpdd on the P-3 radars, but soon after the U.S. Navy’s first exercises with Gotland, the priority changed; MH-60R became the first airborne platform, the P-8A the second.

The Telephonics APS-153 radar uses Arpdd technology and will replace the same company’s APS-147 on new and retrofitted Romeos. A contract for 160 production radars, for U.S. Navy and Australian aircraft, was issued in April 2012. Initial operational test and evaluation was completed in the third quarter of 2013, according to a DOT&E report.

Navy plans for Arpdd on surface ships have changed. Northrop Grumman developed an all-new radar, the SPS-74(V), for installation on aircraft carriers, but only four ships (Vinson, Washington, Stennis and Reagan) had been equipped before the program was canceled in 2013. Now, the Navy plans to build Arpdd technology into the Northrop Grumman SPQ-9B, which will equip Aegis air defense ships as well as carriers.

The U.S. Navy is exploring new ways to combine its ASW assets, and claims some operational breakthroughs after a late-March wargame using Littoral Combat Ships. “Because the systems we are putting on LCS ASW mission modules are very cooperative with the systems we’re putting on guided missile destroyers (DDG), we wanted to pair up the destroyer (with LCS),” says Rear Adm. Thomas Rowden, director of surface warfare. “We found that the whole is significantly greater than the sum of the parts.”

The recent wargames simulated use of the SQQ-89 sonar on guided missile destroyers and the LCS mission package. Rowden says, “When you put two of those working in concert with three helicopters and a single vertical-takeoff-and-landing tactical UAV, you have the ability to a get pretty accurate fixes very fast on the undersea domain. With three helicopters you have a pretty robust capability at range, and with the surface-to-surface missile module we had installed in LCS, you had the ability to reach somebody at range.”

The LCS-plus-destroyer mating for ASW missions proved particularly effective, he says, in operating notional carrier strike group operations. The LCS, “when netted into the carrier strike group networks, allowed the carrier strike group to free up 2-4 guided missile destroyers to do other things.”

The wargames also simulated the effect of swapping LCS mission modules in mid-campaign, according to Rowden. “In the early phases of the conflict, what we really wanted to do was to remove minesweeping gear and install modules that are most advantageous at that point, like ASW to keep track of enemy submarines.”

Unfortunately for the Navy, the ships and aircraft that anchor that expanded ASW potential are all at risk. Defense Secretary Chuck Hagel recently directed the Navy to cut its planned LCS fleet to 32 from 52, and to look for other options to fill the small-combatant ship role. That cut prompted the Navy to significantly reduce the MH-60Rs and MQ-8 Fire Scout vertical-takeoff UAVs the service was buying for those ships.

Still, Navy officials tout other ASW programs in the works to fill in the gaps and perform those missions. Adm. Jonathan Greenert, chief of naval operations, has boasted to Congress this year of ASW combat-system upgrades for DDGs, including improved multi-function towed sonar. The service, he notes, wants to fund additional Mk. 48 Advanced Capability heavy torpedoes, restarting the production line and procuring 105 Mod 7 torpedoes across the five-year defense plan with an eye for future capability upgrades.

Other than the P-8A, only two other high-end ASW aircraft are under development – Japan’s Kawasaki P-1 and an upgrade of France’s Dassault ATL2 NG. Relatively little has been disclosed about the P-1 – the only aircraft designed expressly for land-based ASW since the early 1960s – but features include a 360-deg., active, electronically scanned array (AESA) radar; and Toshiba’s HPS-106, with three sub-arrays in the nose and one aft-facing array in the tail. Sensors and control systems are all Japanese-developed.

After long delays, France awarded a contract to Dassault late last year to update the navy’s ATL2 force. Deliveries are slated to begin in 2018 and end in 2023; the aircraft is expected to remain in service to 2032. Four aircraft are to be delivered by 2019.

The airframe and propulsion system will be largely unchanged, but the mission-processing system will be based on Logiciel Opérationnel de Traitement de l’Information mission software, developed by French shipbuilder DCNS and already in use on ships. Thales will produce the radar and identification friend-or-foe system, based on technologies used in the AESA version of the Rafale fighter’s RBE2 radar. Thales will also produce a new digital acoustic processing subsystem, known as STAN, and L-3 Wescam will provide the MX-20 optronics turret.

DCNS is working on MAC with British partners, and in the framework of the November 2010 Lancaster House Treaties, Jean-Marie Dorbon, innovative and bid director in the surface ship division at DCNS, tells Aviation Week that DCNS is looking at MAC applications for surface ships. Basically, one surface ship sends out an acoustic ping which would bounce off the submarine and be received by a second ship. The second ship remains passive and can approach the submarine without being detected, he explains. The receiving ship may also be in an area where the water pressure, temperature and salinity (the three issues which affect underwater acoustics) allow it to “hear” better than the emitting ship.

DCNS is developing a novel approach to detect ultra-quiet submarines: a system to detect, analyze and locate transient noises such as the spin-cycle of the washing-machine onboard a modern submarine or a tool dropping onto the floor, which are now louder than the vessel’s engines. A demonstrator is already at sea.

Experimental non-acoustic technologies at DCNS include a system to note changes in the bioluminescence exhibited by a variety of oceanic organisms, from bacteria to large squids and fish, which have been disturbed by the passage of the submarine. The shipbuilder is also looking at the possibility of installing MAD on unmanned air or surface vehicles launched from warships.

With Dan Katz in Washington.