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The command and control of air operations places a premium on  connectivity. Having responsive tools and communications to this end is a sine qua non for mission success.

The numbers speak for themselves. When it is fully deployed, NATO’s Air Command and Control System (ACCS) will cover ten million square kilometres of NATO’s European territory. ThalesRaytheonSystems, the consortium that is rolling out the ACCS across all of NATO’s European membership (except the UK), states that the ACCS architecture, which comprises an ensemble of software and hardware will be used by the alliance for everything from day-to-day monitoring of national airspace to the planning and execution of high intensity air operations both within and without NATO as a result of its deployable elements. Furthermore, the ACCS infrastructure deployed in each of these member states will federate a country’s disparate ground-based air surveillance radars to form a single, national Recognised Air Picture (RAP). This RAP can in turn be shared with other NATO members and merged into a single ‘Super RAP’ of NATO’s European airspace. It is clear that this will greatly increase the alliance’s situational awareness, especially when confronting any large scale air offensive developing across much of its territory.
Although the contract for the ACCS was signed in 1999, work is still ongoing. As noted, the ACCS will provide a single, scalable suite of hardware and software, which can be tailored to the needs of NATO members and the alliance as a whole. Two main architectures comprise the ACCS concept – The ARS (Air Control Centre, RAP Production Centre and Sensor Fusion Post) and the CAOC (Combined Air Operations Centre). The ARS is designed to support air control to safeguard a country’s airspace, or the airspace over a defined area in a deployable context. It receives information from sensors, principally ground-based air surveillance active and passive radars (see below) and consolidates this into the RAP so that control of this airspace can be exercised. The CAOC, on the other hand, is the ‘war fighting’ element of the ACCS. This will not only support the command and control of air operations either unilaterally or multilaterally in support of larger joint operations, but it will enable the production of the Air Tasking Order (ATO). The ATO forms NATO’s ‘sheet music’ for air operations. It details all air operations to be performed in a particular theatre over a 24-hour period. This includes all combat air patrols, close air support, battlefield interdiction, tanker and Airborne Early Warning (AEW) orbits, and combat search and rescue coverage to name just five distinct missions. Effectively, the ATO transforms the commander’s intent into action.

The USAF CAOC at Al Udeid airbase in Doha, Qatar is responsible for managing air operations in the US Central Command’s area of operations. Similar NATO facilities are being upgraded through the ACCS initiative. (Photo: US DoD)

NATO is procuring four distinct configurations of ACCS: These include ARSs and CAOCs, plus their deployable equivalents (DCAOC and DARS). ARS centres are being rolled out across 12 sites for the first part of the ACCS initiative. These will be received by Belgium, Czech Republic, France, Germany, Greece, Hungary, the Netherlands, Norway, Poland, Portugal, Spain and Turkey. In addition, NATO will receive a fixed CAOC and a deployable system will be built and based at Uedem, western Germany. A DARS has been delivered to NATO as part of this initiative and is based at Nieuw-Milligen airbase in eastern Netherlands. Combined CAOCs and ARS, imaginatively called CARS, have been installed at the Poggio Renatico airbase in northern Italy and at Lyon Mt. Verdun airbase in eastern France. The second phase of the ACCS initiative will see additional ARS centres being installed in Albania, Bulgaria, Croatia, Estonia, Germany, Hungary, Iceland, Latvia, Lithuania, Slovakia, and Romania. Here, the deployable elements of ACCS are particularly interesting. As NATO-led operations in Afghanistan showed, the alliance is no longer called upon to deploy forces exclusively to its own ‘back-yard’. Operation Deliberate Force (ODF), the Alliance-led initiative in 1995 to undermine the military potential of Bosnian-Serb forces in Bosnia-Herzegovina, was a wake-up call. Reflecting on the C2 of the “Deliberate Force” air campaign, Colonel Christopher M. Campbell of the US Air Force (writing in Col. Robert Owen’s edited volume “Deliberate Force: A Case Study in Effective Air Campaigning”) wrote that the CAOC facilities, from which the operation was conducted at Aviano airbase in northern Italy, “did not adequately support planning requirements for a dynamic operation such as Deliberate Force.” He continued that “the CAOC lacked a central command facility … Further, it lacked adequate communications.” Fortunately, ODF achieved its strategic goals, although his observations underline just how important satisfactory CAOC facilities are to the conduct of a large-scale air campaign. NATO’s possession of a deployable CAOC will ensure that such shortcomings can be avoided in all future operations.

The Sensors

The sensor integration integral to the ACCS underscores the complexity of the initiative. Up to 48 different types of radar will be linked into the overall architecture. The ACCS software alone includes 12 million lines of code. Taking just one country as an example shows the magnitude of the task. Portugal’s Força Aérea Portuguesa (Portuguese Air Force) currently operates eight ground-based air surveillance radars. These include three Hughes/Raytheon HR-3000 HADR S-band (2.3GHz to 2.5GHz/2.7GHz to 3.7GHz) and two Lockheed Martin AN/TPS-44 L-band (1.215GHz to 1.4GHz) ground-based air surveillance radars. Add to this, the radars that the Flyvevåbnet (Royal Danish Air Force) has to integrate. These comprise 24 Thales RAC-3D C-band (5.25GHz to 5.925GHz) deployable ground-based air surveillance radars, which are operated by the Hæren (Danish Army) to provide battlefield air defence, while a single Selex/Leonardo RAT-31S S-band and eight BAE Systems S-743D MARTELLO L-band radars provide national airspace coverage. Beyond the national assets discussed above, the ACCS architecture will have to integrate sensors owned by NATO.

These include the two ERA Vera-E passive radars acquired by NATO under a US$18M deal in 2014 and delivered between 2016 and 2017, plus the two Indra LANZA-LTR-25 L-band ground-based air surveillance radars. Both radars support the deployable elements of the ACCS, notably the DARS. Moreover, ACCS will link not only federate the ground-based air surveillance elements owned by European NATO members, air platforms will be added to the architecture. Whether it is a Armée de l’Air (French Air Force) Dassault RAFALE-B/C equipped with a Thales RBE-2 X-band (8.5GHz to 10.68GHz) fire control radar, or a NATO Boeing E-3A SENTRY using its Northrop Grumman AN/APY-1 S-band (2.3-2.5/2.7-3.7GHz) AEW radar to watch the skies for potentially hostile aircraft, or to manage the air battle, such information will need to be shared with the ACCS.

NATO’s E-3A SENTRY aircraft are one of a multitude of platforms that will be connected to the ACCS architecture via the Link-16 TDL. (Photo: NATO)


This is done using NATO’s standard Link-16 Tactical Data Link (TDL) used for the transmission of track and tactical information between aircraft, and between aircraft and ships or ground deployments involved in the air battle like surface-to-air missile batteries. Link-16 uses a waveband of 960 megahertz to 1.215GHz. Compared to civilian telecommunications, the TDL can move a fraction of the data one’s smartphone handles at rates between 2.4 kilobits-per-second (kbps) to 16kbps. It is a legacy system, having been in service since the late 1970s/early 1980s. Nonetheless, it shows no signs of retiring and is in as much demand now as ever. The reason for its longevity is quite simply that it does the job. Bart van der Graaf, Thales’ Director of Operational Business Development, says that, from an air battle management perspective “Link-16 is still more than sufficient to generate a common operating picture.” However, he is now thinking about what could supplement or replace the TDL over the long-term “I would like to move towards a composite tracking network. Every sensor and effector would disseminate their role and track data into a service-oriented architecture network.”

The OPAL network developed by IAI has been in service for 15 years and takes an innovative “cloud” approach to managing air operations. (Photo: IAI)

The beauty of such a network would be that sensors, platforms and effectors could access this as and when they needed to share data. This would be a step-change from the modus operandi of Link-16. The TDL uses a Time Division Multiple Access (TDMA) approach. In plain English, this is a ‘roll call’ system. Each Link-16 network includes a central node controlling it and all the participants. The node will ask each participant in sequence if it has any information to transmit to other participants, and will share any information destined for that participant. The node will perform this roll call several times a second covering all of the participants. However, the approach Mr. van der Graaf is promoting would see participants only sharing and receiving information when they need to. The key difference is that a Link-16 node will consult all of the participants when ‘doing its rounds’ regardless of whether they have any information to share or receive. The key attraction of Mr. van der Graaf’s approach is that it helps to preserve that important commodity in communications, namely bandwidth. He adds that it would enable the network to expand and contract according to its number of participants, again helping to save bandwidth. Mr. van der Graaf is emphatic that the world of air battle management needs to look beyond Link-16 “We have to look at what is coming after. It is about time as this technology is from the 1970s. We have to get away from a TDL mindset and look at a service-oriented approach.”

The Cloud

Israel Aerospace Industries (IAI) have adopted such an approach with its OPAL air battle management system, which it unveiled in April 2019. At the core of OPAL is a communications network, which all participants – be they conventional aircraft, unmanned aerial vehicles, ground vehicles, ships or troops – can access. Participants can then view a common operating picture, which is shared across the OPAL network. Tactical data can be shared too, in much the same way as it is currently with TDLs such as Link-16. One of the interesting attributes of OPAL is that while Link-16 et al can share track data, OPAL can make the full operational environment visible to all participants. One key attraction is that existing communications can be used to access OPAL removing the need to outfit platforms with new radios. IAI shared with the author through a written statement noted that “OPAL relies on a variety communication means and technologies such as radios, satellite communication and even ground Ethernet connectivity.”

The Link-16 TDL has been placed in the hands of troops through systems such as Viasat’s BATS-D. This is a handheld system allowing soldiers to connect to Link-16 networks. (Photo: US DoD)

The network can share a mind-boggling quantity and diversity of information, which “ranges from tactical mission data, platform inventory, video and images, intelligence data and even weather conditions.” The architecture is flexible allowing it to easily scale-up or down according to the number of network participants and the information they are sharing “OPAL is highly dynamic and allows for a highly agile operational methodology vs. the somewhat rigid nature of Link 16,” IAI continued. Interestingly, IAI does not necessarily see OPAL replacing Link-16 but rather as complementary as it can “extend Link-16 communications to non-Link-16 entities and thus ensure overall force interoperability.”
This company has taken a leaf from the civilian telecommunications world, particularly regarding smartphones, in its development of OPAL“Once an operating system has been certified for a specific hardware (for example, a specific phone) then new applications can be simply installed without risking the overall deployment. As this is quite common in the mobile phone market, it is quite unique in the defence arena.” It may surprise readers to know that, despite IAI’s recent announcement OPAL has been in service for a number of years “OPAL has been operational for more than 15 years in several armed forces. During this time, it has constantly evolved to include more capabilities and was installed on dozens of different platforms.”

Air operations are unlikely to reduce in complexity in the near future. Platforms such as the Lockheed Martin F-35A/B/C LIGHTNING-II are sensor rich and can gather an unprecedented quantity of information. These aircraft, and their other fifth-generation counterparts, will share the skies with a host of other platforms such as UAVs, smart munitions and missiles, which can gather and distribute data. The upshot of this is that a torrent of zeros and ones will be generated that will need to be managed and shared. New architectures such as ACCS highlight the enormity that the challenge of connectivity on such a large scale. For now, air forces can rely on legacy TDLs like Link-16 to carry this information. Future air operations will almost certainly depend upon wider bandwidth and more agile communications to share information to the fullest extent possible. This will ensure that situational awareness and hence ‘command and control’ is as timely and accurate as possible during air operations moving at the speed of relevance.

Thomas Withington is an independent electronic warfare, radar and military communications specialist based in France.