Integrating allied air and missile defence systems

NATO faces a complex challenge: how to rapidly enhance its air and missile defence capabilities while ensuring integration across disparate systems developed by various countries. This analysis explores how divergent approaches to integration can be reconciled to create effective multi-layered protection against sophisticated aerial threats.

In the wake of the conflict in Ukraine, the subject of integrated air and missile defence (IAMD) has seen a surge of interest within NATO. Projects such as the German-led European Sky Shield Initiative (ESSI), which has the stated aim of coordinating and accelerating the procurement of air and missile defence systems are illustrative of this newfound prominence.⁽¹⁾ A potential surge in the capacity for IAMD at the disposal of NATO’s European members has the effect, however, of making questions regarding the integration of capabilities at the Alliance level an even more pressing consideration. Gaps in the integration of capabilities have long been considered consequential by both military practitioners and analysts and a growth in the scale of NATO’s IAMD which may be driven by the procurement of heterogenous off-the-shelf capabilities will potentially increase the complexity of this challenge. It is thus of considerable importance to analyse how the Alliance’s IAMD capabilities can simultaneously be grown at pace and made coherent.

Visions of air and missile defence procurement and coordination

Broadly speaking, there are two approaches to the generation of additional capacity for air and missile defences within Europe. The first approach, exemplified by the ESSI, emphasises the procurement of off-the-shelf capabilities, many of which will be non-European in provenance. This has the potential to allow European states to leverage the defence industrial capacity of states including the US, South Korea and Israel, among others – a decided advantage in a context where pipelines for the production of complex weapons will likely remain congested for some time.

However, this comes at a cost with respect to both security and integration. While many of the systems which can be procured from Allied nations can be linked to other Allied platforms through networks such as Link 16, low-latency data sharing for tasks such as cooperative engagement requires higher-frequency (and often bespoke) datalinks. Moreover, the battle management software employed by different systems is often not compatible, as was illustrated by the longstanding challenges related to sharing data between Aegis and non-Aegis vessels within NATO.⁽²⁾ Finally, there have been residual debates regarding the security implications of linking non-NATO platforms into Allied networks, which caused the German procurement of the Israeli Arrow-3 to be a subject of some controversy.

The second approach, proposed as an alternative by nations such as France, focuses on the production of IAMD capabilities within Europe, with projects such as HYDIS² and TWISTER, two PESCO projects focused on delivering counter-hypersonics via a space-based tracking layer and an endoatmospheric interceptor.⁽³⁾ The advantages of this approach must be juxtaposed with lead times to deliver capability and potential challenges with respect to achieving economies of scale.

Relatedly, there are several conceivable approaches to IAMD at the NATO level. Per one analysis, these approaches can be grouped into three camps – an integrationist approach based around functional specialisation at the national level and the centralised development of C2 capabilities, a European-led procurement effort, and a federated architecture.⁽⁴⁾

The first approach, while arguably a rational one from a military standpoint, raises important questions regarding national sovereign capabilities. A European-led effort has both the strengths and pitfalls already described. An improved version of the status quo with improvements to Alliance-level capacity for the provision of recognised air pictures, for example, would be less constraining but would also limit the degree to which any system could be described as being truly integrated – which will be a particular challenge against complex manoeuvring targets such as hypersonic threats. On the other hand, the engagement of certain targets is likely to become an all arms challenge in which sensors not necessarily held by air defenders are relevant. An example of this might be the classification of unmanned aerial vehicles (UAVs) which will increasingly depend on acoustic sensors in tandem with radar.⁽⁵⁾ As such, a degree of system level heterogeneity should be expected in any case.

The best way forward is, ironically, to do away with integration as a catch-all term. Rather than speaking of an integrated air defence network it might be more reasonable to describe parallel integration efforts which focus on the sensors and effectors most relevant to specific parts of the threat spectrum. This is counterintuitive given the emphasis placed on creating a single seamless system in most discussions of IAMD. However, as illustrated by programmes such as the US Air Force’s Airborne Battle Management System, an excess of ambition can doom integration efforts. Moreover, despite there being truth to the idea that clearly-defined parts of the threat spectrum which could be distinguished by speed and altitude are being challenged by the emergence of capabilities such as hypersonic threats, which operate at the seams of a stovepiped system, there are still parts of the threat spectrum which share few sensors and effectors. For example, few capabilities are relevant to both counter-UAV (C-UAV) and ballistic missile defence (BMD). Similarly, the requirements for latency and sensor fusion differ across parts of the threat spectrum, with tasks such as BMD depending on low latency and a limited number of radar-based sensors while tasks such as C-UAV involve a larger number of sensors but less stringent requirements.

The imperative, then, is not to do away with integration but rather to group capabilities into parallel lines of effort defined in terms of criteria such as network latency, range and altitude categories. This in turn can enable a hybrid approach which will prove better-suited to NATO’s needs than a single approach to force development and Alliance-level integration.

Different approaches to creating architectures

Broadly speaking, there are several types of architecture which can deliver an integrated system of systems. The first involves the setting of specific requirements that link individual systems to one another in well-defined kill chains. An example of this would be the US Navy’s Naval Integrated Fire Control-Counter Air (NIFC-CA), which was built around five pillar programmes (JLENS, Aegis, F/A-18, E-2D and SM-6), into which specific requirements were inserted by the NIFC-CA programme office in order to create well-defined kill chains (for example between F/A-18 and Aegis). The approach taken with NIFC-CA did not confer upon the programme office the capacity to procure, merely to set standards. This approach created a system that was difficult to scale given the very specific standards introduced into each programme, but it nonetheless created an effective Navy-wide network for achieving specific tasks.⁽⁶⁾

The utility of this approach is most likely to be felt when the number of systems relevant to a task is not likely to radically increase. An example of such a task is BMD. The sensors needed to track exoatmospheric targets with resolution sufficient to enable interception by a kinetic kill vehicle either outside the atmosphere or upon re-entry are typically highly bespoke systems such as the X-Band AN/TPY-2 Radar used by the THAAD system, or the ELM-2080S Super Green Pine L-band radar which supports the Arrow-3 system. Moreover, a relatively limited number of systems carry BMD effectors capable of engaging medium-range ballistic missile (MRBM) and intermediate-range ballistic missile (IRBM) targets. Presently among European countries it is only the Aster-30 B1 NT which provides a counter-MRBM capability in the maritime domain, with SM-6 filling this role for the US Navy, while a handful of land-based capabilities also offer this.

Against IRBMs such as the Oreshnik, the number of available systems is likely to be very limited. By way of an example, the US fields 9 THAAD batteries across the whole force. For BMD at the theatre level, then, the likelihood of national solutions emerging is slim – the choice between national capabilities and multilaterally developed systems is an entirely artificial one. In such a context, where nations and publics can credibly be presented with a choice between hanging together or hanging alone, an approach comparable to that of NIFC-CA may be entirely feasible despite the political challenges which can sometimes undercut integration. Since there are undeniable advantages to lessening dependencies on non-European states, in areas where solutions can only be developed at a pan-European level (and thus the issue of national sovereign capability is less pressing), an effort to co-develop capabilities indigenously as proposed by France, or at least impose stringent standardisation requirements comparable to those used in NIFC-CA, is entirely reasonable.

A second approach to integration is backwards integration via the mechanism of service-oriented architectures (SOAs). An example is BMD Flex, a software package developed in order to link Aegis and non-Aegis destroyers together. BMD Flex is based on an SOA, and can use service application programming interfaces (APIs) to draw data from one system into another, even if they were not designed to work together.⁽⁷⁾ This approach does not necessarily scale, however, given the number of APIs used. An optimal role for a service-oriented architecture is drawing together areas of IAMD where a specific system may have utility against a target which occupies a different part of the altitude spectrum from the one which the sensor is normally optimised against. As an illustrative example, BMD sensors might be integrated into a future counter-hypersonics capability through a service-oriented architecture.

The final approach, which offers the greatest architectural flexibility, is a publish-subscribe model. Publish-subscribe models do not require the source code of a system in order to operate – the broad structure of the data suffices. These models rely on message brokers to translate data across formats based on translation layers. The advantage of this approach is that it can allow the integration of systems never intended to work together at scale. For example, in a July 2021 test at White Sands Missile Range a US Army PATRIOT battery was cued by feeds from a US Marine Corps AN/TPS-80 G/ATOR radar and F-35 despite not being specifically built to integrate with these systems.⁽⁸⁾ However, in order for this to be achieved, a U-2 Dragon Lady had to act as a gateway and data had to be translated at an Integrated Battle Command System (IBCS) engagement operations centre. This speaks to one of the challenges of looser systems – complexity is imposed by the need to move data across networks which operate at different levels of sensitivity. For instance, Multifunction Advanced Data Link (MADL) terminals, upon which F-35 depends, are only carried upon a small number of platforms by design. As a rule, system complexity increases exponentially rather than linearly with the addition of a new network node (the so called N-squared problem).

Furthermore, the requirement to translate data across multiple formats requires centralised processing nodes – which may themselves be targeted. Finally, the larger a system becomes the larger and more complex data packages within it become, in order to route data through a larger network – which in turn drives even greater requirements for centralised processing. Lean data formats exist, but these formats typically pose a challenge for encryption (since encryption requires data to be broken into smaller packets).⁽⁹⁾

Where the loose coupling associated with publish-subscribe models might offer the greatest value, then, is when high latency is acceptable as the cost of sensor fusion at scale. This will be especially true against slow and low-flying targets such as UAVs, as well as subsonic cruise missiles given that the comparatively low speeds of the targets somewhat loosen the demand for latency while the task of tracking elusive targets against clutter and complex terrain raises the premium on sensor fusion.

Different integration approaches which eventually converge

An answer to the question of how European IAMD capabilities should be cohered, then, might be provided by an approach which treats different parts of the threat spectrum differently in terms of the type of integration sought and the method of delivering it employed. Against air-breathing targets such as the 3M-14/3M-54 Kalibr and Kh-101 cruise missile families, as well as one way attack (OWA) UAVs, a procurement approach focused on rapid procurement (even at a cost in heterogeneity) as well as backward integration through publish-subscribe models may prove optimal. Subsonic targets represent the most viable means of attack which Russia can employ at scale for the next decade, since the production of missiles such as the Oreshnik IRBM is likely to be constrained by capacity limitations. Even if Russian production capacity for IRBMs increased to 40 a year – which was the number of 15Zh45 IRBMs used with the RDS-10 Pioneer system (NATO reporting name: SS-20 Saber), the USSR could produce with its much greater industrial capacity – it would be some time before Russia had a large IRBM arsenal.⁽¹⁰⁾

The ESSI, with its focus on off-the-shelf systems thus adds greatest value against more immediately challenging aerial threats. Moreover, latency requirements against high subsonic threats are comparatively limited. Indeed, some subsonic threats will require the integration of sensors not organic to the air defence network in an all-arms effort. In this context, backwards integration through publish-subscribe models of a heterogenous mix of capabilities is an entirely viable approach as has been demonstrated in Ukraine, which has cohered a broad mix of Western and non-Western capabilities.

By contrast, the tracking of MRBM and IRBM targets might represent an area where requirements can either be inserted into programmes as NATO standards or, should standards be improperly applied, a smaller number of systems can be backwards-integrated via a SOA approach.

Finally, there is likely to be more commonality between the tracking of hypersonic threats and ballistic targets with respect to the relevant sensors, particularly space-based sensors, as well as effectors. For example, HYDIS² is meant to deliver both a counter-hypersonic capability and a BMD capability. As such, since there is a more integral relationship between these parts of the defensive architecture and since both involve small numbers of exquisite capabilities, counter-hypersonics and BMD at the theatre level can be cohered via a SOA approach.

As such, there might be two parallel and overlapping approaches to air defence: an off-the-shelf approach to targeting air-breathing threats cohered using publish-subscribe models; and a longer-term effort against MRBMs and hypersonic glide vehicles (HGVs) which could either be standardised and pursued as a European effort or aligned via SOA solutions.

Such a system, it might be objected, leaves stovepipes between air and missile defence. However, this is only partially true. First, as mentioned, the sensors and effectors relevant to theatre BMD and air defence do not often overlap. Moreover, a BMD system which was tightly coupled could still be linked to a loosely coupled air defence network, but could not draw on data from this network. However given that only a limited number of sensors are relevant to BMD, it is unclear that this represents a considerable loss of capability. For example, few GBAD systems could provide useful tracks against an intermediate ranged target. As such theatre BMD capabilities could still provide early warning and tracks against tactical targets (for example SRBMs) for systems primarily built to deal with air breathing threats which might also have a tactical BMD role.

Conclusion

A successful approach to delivering a European air and missile defence capability will have to balance conflicting imperatives. In order to do so, the threat must be broken into its constituent parts. This runs counter to the logic of integration, which tends to encourage analysts to view threats as a gestalt. To be sure, integration remains highly important but a plurality of parallel integrations, each tied a different approach to procurement, might best balance Europe’s conflicting imperatives.

Dr Sidharth Kaushal

Author: Dr Sidharth Kaushal is a Senior Research Fellow at the military sciences team within the Royal United Services Institute (RUSI). His specialisms include Sea Power and Integrated Air and Missile Defence.

(1) Anna Desmeriais. How Sky Shield, Europe’s proposed Iron Dome, would work and why it’s becoming controversial. Euronews. 28/07/2024. https://www.euronews.com/next/2024/07/28/how-sky-shield-europes-proposed-iron-dome-would-work-and-why-its-becoming-controversial

(2) Speech by Rear Admiral Brad Hicks at RUSI Space and Missile Defence Conference 2020 RUSI, London February 27, 2020

(3) OCCAR. HYDIS Programme. https://www.occar.int/our-work/programmes/hydis-programme; Timely Warning and Interception With Space Based Theatre Surveillance. PESCO. https://www.pesco.europa.eu/project/timely-warning-and-interception-with-space-based-theater-surveillance-twister/

(4) Shaan Sheikh. Three Visions for NATO Air and Missile Defence. Warontherocks. August 12, 2024. https://warontherocks.com/2024/08/three-visions-for-nato-air-and-missile-defense/

(5) Jack Watling, Sidharth Kaushal. Requirements for the Command and Control of the UK’s Ground-Based Air Defence. (London:RUSI, 2024)

(6) Sidharth Kaushal, Justin Bronk, Jack Watling. Pathways to Achieving Multidomain Integration for UK Robotic and Autonomous Systems. (London:RUSI, 2023)

(7) Defense Daily. Lockheed Martin, Terma AS’s OA Effort Bringing BMD Capability To European Frigates. Defense Daily. 01/08/2010. https://www.defensedaily.com/lockheed-martin-terma-ass-oa-effort-bringing-bmd-capability-to-european-frigates-2/international/

(8) Kaushal Watling Command and Control for UK Ground Based Air Defence

(9) James Dimarogonas et al., Universal Command and Control Language Early System Engineering Study (Santa Monica, CA: RAND, 2023)

(10) Federation of American Scientiess. Soviet Military Power. 1985. https://irp.fas.org/dia/product/smp_85_ch2.htm. Accessed on 5/01/2025