The F-35 vs. The VHF Threat

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The F-35 vs. The VHF Threat

Amid the debate over the F-35’s effectiveness, Yugoslavia offers some interesting insights into the VHF threat.

The F-35 vs. The VHF Threat
Credit: DoD photo by Marvin Lynchard

The heated and ongoing international debate regarding the combat effectiveness of the F-35 Joint Strike Fighter (JSF) in a highly contested environment has led many observers to question the fighter’s survivability in the face of advanced Surface-to-Air Missile (SAM) systems and very high frequency (VHF) radars. Yet, few have examined the issue closely using lessons drawn from the only incident in which a stealth aircraft was lost in combat; when USAF Lt. Col. Dale Zelko’s F-117 – call sign “Vega 31” – was shot down by a Serbian S-125 (SA-3) SAM system over the then Federal Republic of Yugoslavia during Operation Allied Force on the night of March 27, 1999.

Electromagnetic radiation is known to scatter from bodies smaller than its wavelength. This phenomenon, known as Rayleigh scattering, is often used by F-35 critics to point out that the aircraft could be detected by enemy radar operating in the VHF range, given that some of the aircraft’s geometrical features such as the wing and elevator edges are smaller than the 1-3 meter wavelength within which such radars typically operate. Reportedly, this is also how Colonel Zoltan Dani, then commander of the 3rd Battery of the Federal Republic of Yugoslavia’s 250th Air Missile Defense Brigade, managed to detect, and later down, Lt. Col. Zelko’s plane. According to The Aviationist, a series of in-field modifications carried out by the Yugoslavs further reduced the frequency of the 1960s vintage P-18 VHF acquisition radar under Dani’s command, which enabled his men to detect Zelko’s F-117 at a distance of 30 to 37 miles (50-60 km).

Because of their relatively long wavelength, VHF radars generally lack sufficient accuracy to guide a missile to a target on their own and are therefore used to cue higher frequency, shorter wavelength engagement radars to the approximate location of the target. Narrowband stealth aircraft such as the F-117, F-22 and F-35 were designed to be very low observable (VLO) in these higher frequencies in order to significantly limit the range at which they can be successfully detected by engagement radars. Consequently, despite inputs from the VHF acquisition radar, the X-band* engagement radar of Dani’s SA-3 battery was able to track the F-117 only at a distance of 8 miles (13 km), obtaining a lock and launching two missiles towards it only on the third attempt (the colonel would order his men to switch the engagement radar on for no more than 20 seconds for each attempt in order to avoid being targeted by NATO electronic warfare aircraft).

The advent of powerful, digital active electronically scanned array (AESA) VHF acquisition radars – for example, the Russian ground-based 3D Nebo SVU and Chinese ship-borne Type 517M – enables the detection of narrowband stealth aircraft such as the F-35 at greater ranges. These radars also offer faster and more accurate cueing of engagement radars, enhanced resistance to jamming and –  in the case of ground-based systems – significantly improved mobility over their predecessors. Such systems therefore potentially pose a major challenge to the quick establishment of air superiority; however, a smart combination of the F-35’s capabilities along with supporting platforms and systems could allow the JSF to maintain the upper hand.

Taking a closer look at the F-117 shoot-down incident, it becomes evident that Dani’s successful attempt had a lot more to do with excellent command skills on his part and the appalling use of tactics on NATO’s behalf than it did with the equipment at his battery’s disposal. Apart from the strict emission control mentioned above, the Serbian colonel also frequently used decoys and changed the location of his battery, making it difficult for NATO aircraft tasked with suppression of enemy air defenses (SEAD) to locate and target it. On their part, NATO war planners and pilots made several critical mistakes that proved fatal. These included assigning F-117s the same flight paths on each mission and often using unencrypted frequencies to communicate. Taking advantage of these errors, the colonel would order his troops to monitor NATO communication channels, which, in turn, allowed the Yugoslavs to place the battery close enough to the approximate flight path of the stealth jet, detect it and obtain a lock. Despite being an obvious mistake, unsecure communications are still frequently used by pilots to this day.

Almost equally critical was the absence of effective standoff jamming support from electronic warfare (EW) aircraft during the mission. “The EA-6Bs were too far from the F-117, they may not have been properly aligned with the [enemy] radars…” noted a 2001 Congressional Research Service (CRS) report titled ‘Electronic Warfare: EA-6B Aircraft Modernization and Related Issues for Congress’ that cited David A. Fulgham from Aviation Week. This may come as a surprise to some as by 1999 joint cooperation between stealth platforms and EW assets was not a new concept: Although frequently being portrayed in the media as acting completely on their own, F-117s occasionally received very effective standoff jamming support from EF-111s when attacking targets in the heavily defended Baghdad area during the 1991 Operation Desert Storm. However, the integration of stealth platforms with EW assets into a standard operating procedure did not take place until after Operation Allied Force.

According to the above mentioned CRS report, this was because “the standard operating procedure [was] to withhold F-117s from Air Force exercises and experiments such as “Red Flag.” Thus, important details regarding how EW assets should best be integrated with stealth platforms [were] not universally understood. For example, what frequencies should they work on? Where should the jamming aircraft be positioned relative to the stealth aircraft? Where in the formation should the [Heavy Anti-Radiation Missile] HARM-shooting aircraft fly?” Thus, the “…desire to classify and protect as much information about stealth technology as possible was most likely a factor in the F-117 loss and backfired on the services.”

Nowadays, standoff jamming support for stealth platforms has become standard practice whether the aircraft requires it or not. The importance and benefits brought forth by combining stealth and EW capabilities are well understood and new operational concepts are being developed. Spearheading the development of such a cooperative engagement capability (CEC) is the U.S. Navy with their Naval Integrated Fire Control-Counter Air (NIFC-CA) concept. At the forefront of NIFC-CA is the sensor-rich F-35C acting as an Intelligence, Surveillance, Target Acquisition, and Reconnaissance (ISTAR) platform, channeling data back and providing terminal guidance to standoff missiles launched by other aircraft and warships. Supporting the JSF from a distance will be USN EA-18Gs and F/A-18E/Fs equipped with powerful standoff jammers and long-range missiles, respectively. These two non-stealthy platforms will use data received from the F-35 to jam and engage enemy targets while remaining beyond the reach of enemy SAMs. In the future, the strike package will also include the navy’s low observable Unmanned Carrier Launched Surveillance and Strike (UCLASS) platform which will provide the fighters with aerial-refueling as well as additional surveillance and strike capability.

Managing the strike package will be the task of one or more E-2D airborne early warning and control (AEW&C) aircraft relaying data back to the command and control center on the carrier, to Aegis equipped warships, and to submarines. All platforms are to be networked using secure data-links – these include advanced high-bandwidth, jam-resistant links currently under development –which will grant all members of the carrier strike group a clear and common view of the battlefield, enabling the joint detection and engagement of targets over hundreds of miles. Being able to effectively relay targeting data to standoff weapons through such a CEC would also allow the F-35 to partially compensate for its inability to carry most air-to-surface missiles internally due to the small size of its bomb bays (carrying the weapons externally would compromise the aircraft’s stealth).

The U.S. Air Force is also working on its own CEC; however, the process is complicated since the USAF lacks a dedicated survivable standoff jamming platform of its own, as the slow and cumbersome EC-130Hs it currently operates are unsuited to highly contested environments. The idea that persisted through the 1990s of separating stealth and EW meant that the USAF did not pursue the development of a new dedicated jamming platform following the retirement of its last EF-111s in 1998. This compelled the Air Force to continue relying on the Navy – which did pursue a dedicated EW program as it lacked stealth aircraft of its own – for EW support. In addition to cooperating with the USN, the USAF could also employ its other stealth platforms such as the B-2 and, in the future, the LRS-B and VLO unmanned combat aerial vehicles (UCAVs), to target strategic SAM systems as these platforms offer superior wideband stealth given their combination of geometrical features such as a large size and a tailless configuration, which enables them to maintain their VLO status when confronted by VHF radars.

CECs are not without disadvantages. Concepts such as NIFC-CA are potentially vulnerable to cyber attack and EW. Data-links could be jammed or hacked, Electronic Support Measures (ESMs) such as passive detection systems could attempt to locate aircraft based on their electronic emissions, and long-range anti-radiation missiles, which could be fielded in the 2020s, may be used to target critical assets such as the E-2D in NIFC-CA that channels data back and forth between the aircraft and warships in the carrier strike group. Nevertheless, the flexibility of “network-centric” cooperative engagement concepts allows additional systems and platform to be plugged or unplugged from them as required, offering increased survivability and a lot of growth potential. This means that as new methods of countering the above mentioned threats are developed, they could be easily integrated into new or existing concepts.

It is important to remember that the F-35 is no F-117. Designed with network-centric warfare and joint operations in mind, the JSF offers its pilot unprecedented situational awareness thanks to its ability to communicate and process data obtained from a multitude of both onboard sensors and those located on other platforms. Unlike the F-117, which had no radar, the F-35’s powerful AN/APG-81 AESA is also capable of acting as a narrowband jammer that can be employed if necessary against engagement radars once the jet is deep inside enemy territory. These features make the JSF a key “team player”; its capabilities and potential must therefore be viewed in the context of a CEC or collective system rather than as a single platform. Dynamic, network-centric CECs such as NIFC-CA will become all the more vital over the next two decades as radars and SAMs become increasingly sophisticated. Cooperative engagement will also grow in importance as the U.S. Air Force and Navy improve their interoperability and U.S. allies begin fielding more F-35s and Aegis equipped warships. In a highly contested environment, teamwork and tactics are just as important as stealth.

Guy Plopsky is a Fellow at the Center for Advanced Technology, Tamkang University (Taiwan).  Fabrizio Bozzato is a PhD Candidate at the Graduate Institute of International Affairs and Strategic Studies, Tamkang University (Taiwan).

*Corrected from “S-band.”