There are three primary ways to find a submarine that does not want to be found. You can listen for sounds, you can find it magnetically (something like the way compass needles find north), or you can locate a surfaced sub with radar. Since sound waves can travel a long way underwater, a sub's most important "signature" is acoustic. But how can an aircraft noisily zooming through the sky listen for a submarine gliding beneath the waves? The answer, developed during World War II, is the sonobuoy. This is an expendable float with a battery-powered radio and a super-sensitive microphone. "Passive" sonobuoys simply listen. "Active" sonobuoys add a noise-makerthat sends out sound waves in hope of creating an echo. By dropping a pattern of sonobuoys and monitoring them, an ASW aircraft can spread a wide net to catch the faint sounds of the sub's machinery, or even the terrifying "transient" of a torpedo or missile launch.
Another detectable submarine signature is magnetism. Since most submarines are made of steel, they create a tiny distortion of the earth's magnetic field as they move.[55] The distortion is very small, but it is detectable. A "magnetic anomaly detector" (MAD) can sense this signature, but it is so weak that the aircraft must practically fly directly over the sub at low altitude to do so.[56] In order to isolate the MAD from the plane's own electromagnetic field, it is mounted on the end of a long, retractable "stinger" at the tail of the aircraft.
Eventually, every submarine must come to periscope depth to communicate, snorkel, or just take a quick look around. Although periscope, snorkel, and communications masts are usually treated with radar-absorbing material, at close range sufficiently powerful and sensitive radar may obtain a fleeting detection. Finally, there are more conventional means of detection. For example, an airborne receiver and direction finder may pick up a sub's radio signals, if it is foolish or unlucky enough to transmit when an enemy is listening. And sometimes the telltale "feather" from a mast can be seen visually or through an FLIR system.
The integrated ASW package of the initial version of the Viking, the S-3A, was designed to exploit all of these possible detection signatures. Sixty launch tubes for sonobuoys are located in the underside of the rear fuselage. In addition, the designers provided the ASQ-81 MAD system, an APS-116 surface search radar, a FLIR system, a passive ALR-47 ESM system to detect enemy radars, and the computer systems that tie all of these together. Once a submarine has been found, it is essential that all efforts be made to kill it. To this end, the S-3 was not designed to be just be a hunter; it was also a killer. An internal weapons bay can accommodate up to four Mk. 46 torpedoes or a variety of bombs, depth charges, and mines. Two wing pylons can also be fitted to carry additional weapons, rocket pods, flare launchers, auxiliary fuel tanks, or a refueling "buddy store."
All this made the S-3A one of the best sub-hunting aircraft in the world, which was good enough in its first decade of service. By 1981, though, the — A model Viking clearly needed improvement in light of the growth in numbers and capabilities of the Soviet submarine fleet. In particular, the improved quieting of the Russian boats made hunting even more of a challenge. In order to improve the S-3's avionics, sonobuoy, ESM and radar data processing, and weapons, a conversion program was started. The result was the S-3B, which upgraded basic — A model airframes to the new standard. The first S-3Bs began to arrive in the fleet in 1987, and they quickly showed both their new sea control abilities and capability to fire AGM-84 Harpoon antiship missiles. This is the version that serves today.
One of the original hopes for the S-3 was to provide a basic airframe for a number of other aircraft types. Unfortunately, the small production run of the Viking has limited its opportunities for other roles. A small number of early S-3As were modified by removing all the ASW equipment and fittings for armament, allowing them to carry urgent cargo and mail and providing seats for a crew of three and up to six passengers (with minimal comfort). Designated US-3A and possessing a much longer range than the normal C-2A Greyhound COD aircraft, a total of five served in the Pacific fleet until they were recently retired. A dedicated tanker version, the KS-3A, was tested in 1980, but never went into production.
The single most important variant was the ES-3A "Shadow," an electronic surveillance (ESM) and signals intelligence (SIGINT) platform, which replaced the venerable EKA-3B "Electric Whale." Externally, the Shadow is quite distinctive, with a prominent dorsal hump and a retractable radome. About 3,000 lb/1,360 kg of ASW gear was removed and 6,000 lb/2,721 kg of electronics were packed into the weapons bay. While the Shadow is unarmed, it can also carry external fuel tanks and "buddy" refueling stores. Sixteen of these aircraft are split between two squadrons: VQ-5 (the "Sea Shadows") in the Pacific Fleet and VQ-6 (the "Ravens") in the Atlantic. Detachments of two or three aircraft normally deploy with every carrier air group, providing ESM, SIGINT, and OTH support for the CVBG. Unfortunately, recent budget cuts have targeted the shadow community which appears to be headed for disestablishment. Plan on seeing the ES-3 head for the boneyard in 1999.
The S-3 community has changed a great deal since the end of the Cold War. As long as the Soviet Union maintained the world's largest submarine fleet, the ASW squadron was an integral part of the carrier air group. But today, that "blue-water" submarine threat has receded. This hardly means that the S-3's can be retired and their crews given pink slips. On the contrary, the VS squadrons have taken on a whole new set of roles and missions, making them more valuable than ever. After the premature retirement of the KA-6D fleet in 1993, they took on still another role, becoming the primary aerial refueling tanker for the CVW. This has not proved to be the best solution to the aerial refueling problem, since an S-3B can only off-load about 8,000 lb/3,628 kg of fuel, as compared to over 24,000 lb/10,886 kg for the KA-6D. With the thirsty F/A-18's needing at least 4,000 lb/1,814 kg every time they go on a long CAP or strike mission, even the ES-3 Shadows are being used as tankers! To reflect all this, the previous ASW designation of their squadrons has been changed to "Sea Control," which uses the "VS" nomenclature.
The S-3B community currently includes ten operational squadrons, administratively divided between two Sea Control Wings: one for the Atlantic Fleet and one for the Pacific. A single Fleet Replacement Squadron, VS-41, based at North Island NAS, California, serves as the advanced training unit. During Operation Desert Shield and Desert Storm, S-3 squadrons flew maritime patrols to help enforce sanctions against Iraq. In fact, the only complaint I've ever heard about this wonderful aircraft is that the Navy bought too few of them. Another two hundred would have been invaluable today, but the poor choices on the part of naval aviation leaders scuttled that idea. At the end of 1997, about 120 S-3's remained in service. Eventually, all of their tasks will be taken over by the future Common Support Aircraft that is scheduled to enter service around 2015.
55
The Soviet "Alfa"- and "Sierra"-class SSNs, along with a few experimental boats, had hulls welded from titanium, a very non-magnetic metal. The Russians can no longer afford the exotic construction methods required to build such boats.
56
This can be as low as five hundred feet, according to some open-source publications. For obvious reasons, MAD performance specs are highly classified.