Counter-drone defence needs a new class: the case for Gap Filler Air Defence

While drones are cheap, modular and quickly available, none of this applies to air defence. Technological change has created an imbalance that cannot be eliminated with existing concepts. Counter-drone defence therefore needs a new, affordable and pragmatic class of defence – a Gap Fill Air Defence. A commentary by Moritz Vischer.

The threat from the air is growing, and high tech has long ceased to be its only basis. Today's drone threat often rests on familiar paradigms, which modern technologies, however, massively amplify. Small, agile and increasingly autonomous systems can be built thanks to additive manufacturing, compact and inexpensive sensors such as MEMS gyroscopes and accelerometers, thermal cameras and powerful batteries. Because production is decentralised, modularity is high and operational experience is fed back quickly, the number of effective and agile drone platforms is growing steadily. Without new thinking in defence, defenders face a tactical and economic imbalance to their disadvantage.

Search, track, engage: the basic functions of defence

Assuming that the basic paradigms of engaging air targets have not changed, it becomes clear what matters now: combining the three basic functions of search, track and engage so that they can be performed as efficiently as possible. Given the large number of potential attackers, resistance to saturation is currently of decisive importance – at platform level as well as at higher levels. The paradox is that precisely the specialisation and growing complexity pursued over decades are now negatively affecting the available quantities and delivery times of the systems.

The struggle between quality and quantity is never finally decided; at the lower end, however, it can be delimited quite well, particularly in air defence. If the search sensor cannot detect small targets, or if the effector's probability of hit and kill is wrongly designed, system performance collapses disproportionately. This cut-off effect is evident, for example, in guns and in jammers.

In principle, the probability of a hit does not depend on calibre. Small calibres, however, lose a great deal of velocity, which limits their range, and even a very high rate of fire is wasted due to dispersion even at short distances. Projectiles without self-destruction also always pose a safety risk (collateral damage). A sufficiently high density of sub-projectiles to destroy very small targets and a much greater stand-off distance only become possible with proximity fuzes or programmable ammunition (in the larger calibres).

This is reflected in the current success of the 30 millimetre × 173 and, more recently, the 25 millimetre × 137 calibres. Other calibres leave the muzzle noticeably more slowly, such as 40-millimetre grenade launcher ammunition and the 30 millimetre × 113 calibre – with very negative consequences, especially with regard to the air defence (Flab) hypothesis. This simple, fundamental and still valid rule of thumb of air defence indicates the effective ranges and the limits of using guns. It follows from the fact that the target's flight path must be predicted during the projectile's time of flight.

For jammers, on the other hand, the cut-off point is currently being reached through fibre-optic drone control or the increasingly AI-supported use of autonomous drones. As a result, the already limited effect of external jamming signals has quickly lost importance.

Affordable, available, adequate: a gap in counter-drone defence

Condensing these considerations leaves three key words: affordable, available, adequate. It follows almost inevitably that it would make sense to create a new category between the VSHORAD class (colloquially Flugabwehr in German) and CAFAD (Fliegerabwehr). Such a Gap Filler Air Defence category takes account of the lower threshold (cut-off) of the necessary complexity without costs exploding at platform level.

The fact that categories, boundaries and definitions are becoming more fluid in society in general has hugely liberated the development of drones and loitering munitions. This playfulness and openness must now also be brought into the development of adequate and affordable air defence solutions. It is certainly useful to carefully familiarise not only developers but also procurers and users with the advantages, but also the limits, of adequate solutions in the sense of "expectation management".

Provided user safety is maintained, adequate qualification could also noticeably shorten development time. In the end, the courage to accept gaps may well be the key to closing the current gap in air defence quickly and cost-effectively.