The Signal and The Noise

This is an article published in our December 2016 Issue.

It is also imperative for submarines to detect threats in the electromagnetic spectrum when they surface. For this reason, ESMs have been developed which be integrated with a submarine’s periscope. (Saab)

The electromagnetic spectrum is a loud, chaotic place. Navies must use their Electronic Warfare (EW) equipment to listen carefully to tease out the signals of interest from the cacophony of electromagnetic noise littering the littorals and the high seas.

It has was a scenario that naval strategists have been anticipating in lecture theatres, ward rooms and bars since the end of the Cold War, where the scholastic decedents of the celebrated father of naval strategy, the US Navy Admiral Alfred Mahan (1840-1914) cogitate on the future shape of the war at sea. The specific scenario is the attack of a US Navy warship from land using Anti-Ship Missiles (AShM). The very stuff of debate and examination has now become reality. At around 1900 on 9 October, the USS Mason, an ‘Arleigh-Burke’ class destroyer, while underway in international waters in the Red Sea, came under attack from two AShMs. The destroyer had deployed there on 3 October, following an AShM attack on the HSV-2 Swift catamaran operated by the United Arab Emirates National Marine Dredging Company on 1 October, by a suspected China Haiying Electromechanical Technology Academy (CHETA) C-802 family AShM. The USS Mason was part of a three-ship deployment which also included the USS Nitze, one of her ‘Arleigh-Burke’ class sisters, and the USS Ponce, an ‘Austin’ class amphibious assault ship.

The bewildering array of antennae mounted on a warships’ masts betrays how important the electromagnetic spectrum is to contemporary naval operations. (Saab)

The US Navy has declined to state what missile types were employed during the attack on the USS Mason, however it has shared that the two missiles crash-landed harmlessly in the sea some distance from the warship. Understandably, it has declined to state whether this was the result of action on the part of the USS Mason, fire control errors on the part of those whom launched the AShMs or design/engineering errors on the part of those who developed the missile. Nevertheless, it is known that the weapons were fired from the vicinity of the Bab el-Mandeb Strait, a stretch of the Red Sea flowing past the west Coast of Yemen. The US Navy states that the AShMs were fired from Yemeni territory under the control of the Houthi Shia Muslim militias; one of the belligerents involved in the Yemeni civil war.


According to the US Naval Institute (USNI), a non-for-profit professional organisation based in Annapolis, Maryland, once the USS Mason had detected the incoming missiles, it fired two Raytheon RIM-66 Standard Missile-2 (SM-2) family Surface-to-Air Missiles (SAMs) at the incoming threat. The US Navy has not expanded upon which RIM-66 SM-2 variant was used in the engagement, although it could have been the RIM-66M5 SM-2MR Block-IIIB version. A single Raytheon RIM-162 ESSM (Evolved Sea Sparrow Missile) was also launched from the ship to engage the missile; the first time this weapon has been used in combat according to the USNI. Of interest to this article is the fact that the USS Mason was also said by the USNI to have deployed BAE Systems’ Nulka missile decoys to spoof the incoming AShMs. Open sources state that the Nulka decoy is specifically designed to spoof radar-guided AShMs, continuing that the decoy transmits Radio Frequency (RF) signals and performs a flight trajectory mimicking a large ship in such a fashion as to lure the AShM away from its original target. The employment of the Nulka also provides us with a clue as to what type of AShMs were employed in the attack.

As we know, the USS Mason fired Nulka decoys to spoof the incoming AShMs. This suggests that both the missiles were known to be, or strongly suspected of being, radar-guided. The exact missile type is open to debate. Some sources suggest that the USS Mason may have been targeted by the Chinese Hongdu Aviation Industry C-101 AShM. Other sources dispute this, and state that the missiles involved were either China Precision Machinery Import and Export C-801 or C-802 family AShMs. Speculation has stated that the Houthi militia alleged to have fired the AShMs may have received such weapons from Iran. Research performed by the Stockholm International Peace Research Institute, a non-governmental organisation based in Stockholm, Sweden, shows no record of Iran, or Yemen, receiving the C-101 weapon, although it does note that Iran has received both C-801 and C-802 weapons last decade and in the 1990s, with Yemen having received 25 C-801 AShMs from the People’s Republic of China in 1995. What is not in dispute is that all of these AShMs employ Active Radar Homing (ARH) seekers, by which the missiles employ a radar to locate their target, usually operating in Ku-band (13.4-14/15.7-17.7 gigahertz/GHz) according to some sources for the C-101 and C-801, and possibly X-band (8.5-10.68GHz), sources continue, for the C-802.

Spectrum Warfare

The firing of the Nulka decoy was almost certainly triggered by the USS Mason’s Raytheon AN/SLQ-32(V) family electronic warfare suite. Put simply, the AN/SLQ-32(V) detects hostile radar signals, such as those being transmitted by AShMs, and then triggers the launching of decoys such as the Nulka (see above) to spoof the incoming threat. The incident on the Red Sea on 9 October underlines the importance of EW to navies around the world. Todd Caruso, low observable tactical aircraft business development manager at BAE Systems, argues that naval EW: “represents the ability for (navies) to control and dominate the electromagnetic spectrum. Control of radar signals, radio signals and infrared signals across the spectrum enable (navies) to sense, protect and communicate. At the same time, (naval EW) can be used to deny adversaries the ability to either disrupt or use these signals.”

At its core, naval EW is focused on enhancing the situational awareness of a ship’s crew in their locale. Ole Frandsen, Terma’s manager of C2 (Command and Control) applications, and C2 and sensor systems, told AMR that: “Naval picture compilation is the backbone of every kind of naval operation; even the execution of the most simple surveillance mission requires some sort of maritime awareness.” Terma provides its C-Guard Decoy Launching System has been supplied to in excess of 100 navies globally, Mr. Frandsen notes. This maritime awareness includes RF signal detection which: “provides an additional layer of information in the picture compilation process and offers (crews) the ability to classify and locate RF emitters.”

 C-Guard decoy
Terma’s naval electronic warfare products include the C-Guard decoy launching system, as shown here. Decoys have a vital role to play in spoofing the radars of incoming anti-ship missiles. (Terma)

Signal detection forms one vital part of naval EW. As a written statement supplied to AMR by Saab notes, signals must be: “classified and identified and the direction from which they originated measured thus providing valuable information for the situational picture. When coupled with a database of possible threat emissions the (naval EW systems) can rapidly determine whether the signals originate from a hostile, friendly or neutral source. Saab already provides a host of naval EW products, such as the firm’s USME family (Underwater and Surface Maritime Electronic Support Measure), and its Naval Laser Warning Systems and Communications ESM systems, although the company declines to mention exactly which vessels, and with which navies, these systems are in service with.

Littoral Challenges

Today, naval EW practitioners face distinct challenges regarding maritime operating environments. As the engagement of the USS Mason illustrated, navies can experience hostile actions in the littoral adjacent to the shore. To the naked eye, on calm and bright days, such environments can appear as havens of tranquillity, yet vis-à-vis the electromagnetic spectrum, they be raucous and cluttered. Pleasure craft, trawlers and commercial vessels can all be transmitting radar and communications signals. Added to this, civilian cell phones may still be capable of working at distances of up to 12 nautical miles (15 kilometres) from the shore. To illustrate the complexity, as well as being employed by AShM ARHs as illustrated above, Ku-band transmissions can be used for civilian Satellite Communications (SATCOM). The challenge for naval EW practitioners is to detect and discriminate a Ku-band transmission from a missile amidst the mass of other, entirely innocent, electromagnetic transmissions which may occur in a vessel’s locale. As Saab’s statement continues: “It is not unusual for ESM equipment to (detect) 150 or more emitters at any time while operating in the littorals,” adding that: “Littoral operations present a new challenge with the ever increasing expansion of the mobile telephone networks.”

Harris’ naval EW products include its ES-3601S (pictured here) and ES-3601U products. The firm has notable expertise in the detection and identification of hostile radar signals. (Harris)

Alongside the challenge posed by the littoral environment, the design characteristics of RF emitters such as naval surveillance radars are challenging naval EW system engineers. Harris has been involved in the naval EW field since the early 1980s. Today, it has a significant naval EW systems portfolio which includes the ES-3601S/U Tactical Radar ESM and Surveillance System which can detect hostile RF signals in the two gigahertz to 18GHz waveband, encompassing the bandwidths used by most naval surveillance radars and ARH seekers. Similar bandwidths, with the option to increase these downwards to 0.5GHz and upwards to 18GHz are offered by Harris’ ES-3701S/U Precision Radar ESM System Family; to name just two. Radar technology, as noted by Harris’ Uri Lifschitz, is challenging naval EW practitioners and engineers: “The use of advanced, phased-array antennae are becoming common-place among modern, military radar designs.” Basically a phased array radar produces RF energy at one source, and then transmits this through several radiating elements positioned across an antenna. This process allows the radar’s beam to be ‘steered’ across an azimuth of circa 120 degrees using a process known as constructive/destructive interference. Space is insufficient here to discuss the workings of phased array radars in detail however, such radars produce low side lobes. Side lobes are residual RF transmissions which radiate out either side of a radar’s main beam which can be used to detect a radar’s transmission without being directly in the radar’s line-of-sight.

To further complicate matters, Mr. Lifschitz continues that such radars employ “pulse-to-pulse frequency agility over very wide RF bandwidths and arbitrary, not patterned, scanning of the target’s azimuth and elevation space.” What this means in practice is that radars do not perform sustained transmissions on a single frequency, instead changing their transmission frequencies at a rate of milliseconds across a wide frequency range. This makes the radar’s signal become a needle in an electromagnetic haystack of noise, such as the littoral environment discussed above. Moreover, such changes of frequency maybe performed in a pseudo-random sequence to frustrate the attempts of naval EW practitioners to identify a radar by its transmission parameters. As if this was not complicated enough, Mr. Lifschitz adds that today’s naval surveillance radars can employ so-called Low Probability of Intercept (LPI) techniques, which usually see them employing very low power transmissions, once again to hide their signals in the morass of electromagnetic noise.

The assessments of Mr. Lifschitz chimes with those of Elbit Systems’ Elisra subsidiary. The company has a long track record in the provision of naval EW systems, both for the Israeli Navy, and other naval forces around the world. The company told AMR via a written statement that it believes future naval EW systems will: “have to cope with future threats and scenarios and will provide answers for threats in the forms of wider frequency coverage, higher sensitivity and accuracy.” The firm adds that such challenges maybe met through the application of increasingly sophisticated software: “In order to cope with the future challenges EW systems will have to employ advanced real-time machine learning algorithms to provide reliable and high resolution EOB (Electronic Order of Battle) pictures.” In essence, EW systems will need to learn from the electromagnetic environments that they have observed in the past, and look for similar signal characteristics, or behaviours, in the environments that they are experiencing at that moment.

Aqua Marine system
Elbit’s naval EW products include its Aqua Marine system which has a digital and modular design. The product is believed to be in service with the Israeli Navy. (Elbit Systems)


What does the future hold for naval EW? As with much of the EW domain more generally, in the land and air spheres, experts such as Mr. Caruso foresee a convergence of cyber warfare and EW capabilities. The naval battles of the future will be fought in a digitised environment where information is passed between navies using satellite as well as conventional radio communications. Such information will encompass everything from still or video imagery of targets, radar track information, written messages and voice communications. Thus naval EW efforts will not only be focused on trying to protect ones’ use of the electromagnetic spectrum, while denying it to others, but also to employ electronic warfare in such as fashion to protect one’s own use of the electromagnetic spectrum, while denying it to one’s adversary, for the flow of information.

It is also imperative for submarines to detect threats in the electromagnetic spectrum when they surface. For this reason, ESMs have been developed which be integrated with a submarine’s periscope. (Saab)

At the market level, naval EW systems are expected to be in demand in the coming years. IQPC’s publication Naval Combat Systems: Trends and Analysis Report 2016 states that of the key informants that the firm contacted to compile its report, “Almost half (48 percent) indicated that electronic warfare systems would be a priority in the future.” This is because, the report continued: “Navies are continuing to invest in new electronic attack technologies to counter advanced radar threats … The market for naval EW systems alone is forecast to exceed $10 million over the next decade.” This demand has clear implications for the Asia-Pacific: The same report noted that 78 percent of respondents believed that the Asia-Pacific region would be the most attractive global market for naval combat systems procurement over the next ten years.

by Thomas Withington