It’s heartening to see the surge of symposiums, round tables and columns on ‘The changing character of War’. Most conversations are centred around multi-domain warfare (MDW), whole-of-nation responses and the drone revolution. Our view, however, is starker – ‘deep tech is driving a discontinuity’, not a slow, linear shift. Look back and it feels closer to the arrival of cavalry, gunpowder, fixed defences and later manoeuvre warfare, moments that reshaped how wars were conceived and fought. Back in 2021, in the ‘Contours’ column in Defstrat.com, I argued that technology is reshaping the battlespace, upending traditional wisdom, breaking battlefield linearity and exposing the limits of several legacy platforms. With that in mind, T4, the Think tank is launching a new series (with podcasts to follow) that re-examine core concepts in light of today’s tech reality. We begin with a first principles look at ‘Defence’, what to preserve, what to discard, and what to rebuild for a sensor-saturated, precision-heavy war. It is our considered opinion that ‘Doctrines must change before the enemy forces them to’.

Technology is eroding the logic of traditional defensive concepts built around fixed lines, fortifications (and logistic dumps), and a decisive reserve for counterattack. Persistent sensors (satellites, radars, swarms of small drones) spot movement quickly; precision weapons (loitering munitions, glide bombs, long-range rockets) hit deep targets without breaching the front; and electronic warfare and cyber-attacks disrupt radios, GPS, and command posts.  In this environment, a fortified line is more like a beacon, and large, static stockpiles are more like lucrative, accessible targets for long range missiles and munitions, as they can be mapped, targeted and struck at a time of the attacker’s choosing.

Two years back, in ‘Contours’, we had suggested that in defence the ratio between the ‘holding’ element and ‘reserve’ should be reversed, i.e. hold lightly, but make the reserve stronger to retain flexibility. Warfare, however, is changing faster than most defensive ideas can adapt. Cheap drones, precision missiles, loitering munitions and aggressive electronic warfare have shrunk both distance and time in the kill chain. An attacker no longer has to break through a front to hurt what lies behind in depth; he can hit HQs, ammunition and fuel dumps, bridges, communication nodes and installations in depth. In recent conflicts, small FPV drones have harassed armour and artillery; long-range Kamikaze UAVs have struck depots hundreds of kilometres away; and glide bombs released from stand-off have struck fixed positions that could neither move nor hide. In such a situation, the classic picture of strong defensive lines with deep fortifications and a large mobile reserve no longer suffices. Defence must move from lines to systems – layered defences, resilient networks that protect people, vital areas and processes across the entire depth.

Holding the line is therefore not enough. The defender’s dilemma is simple- even if forward troops and obstacles hold firm, the hinterland can be devastated by drones and long-range precision fires. Persistent surveillance implies movement is seen quickly and targeted even faster. One can easily imagine a sector where logistic depots are blown up and bridges are dropped while the trenches remain intact; the forward line in that scenario becomes a trap, starved of supply and freedom to manoeuvre. The attacker enjoys many options; the defender must rethink and reallocate resources to survive the opening blows and still keep the force fighting. The larger question then arises – what is the defender actually defending? If areas in depth, military as well as civilian, remain vulnerable, have we achieved our purpose merely by holding a fortified line?

None of this, however, cancels the basics. Terrain still shapes battle. Obstacles still slow and channelise the attacker if they are covered by observation and fire. Reserves remain vital, but they must be smaller, quicker, multi-axis and harder to detect. Holding territory will continue to be both a political and military necessity; what must change is how we hold it, what we protect first, how we hide, how we move, and how we repair under fire. Protection of targets in the hinterland must begin on Day 1 and not after the first salvos land. In practice this means reducing signatures through camouflage and emission discipline; dispersing logistics into micro-dumps that can be moved and replenished; layering counter-drone and short-range air defence with EW at the front of the stack; and training commanders to operate through disruption with pre-delegated authorities and redundant communication networks. Recent wars have shown that headquarters which emit predictably are found and fixed; convoys that follow routine are ambushed from the air; and batteries that linger are hit by counter-battery fire supported by drones. The remedy lies in changing tactical drills. Hide, move, deceive, and regroup faster than the enemy can target.

So far we have discussed land based defences. What about the other traditional domains? Air. The same logic applies in the air. Traditional threats, combat aircraft and attack helicopters remain, but the munitions they carry and the new profiles of attack complicate air defence. Glide bombs and stand-off missiles approach on difficult trajectories; small drones and rockets present small radar signatures; and low-cost swarms can overwhelm Air defence systems and endurance. Air defence systems today are vulnerable to multiple low-cost threats in addition to the classic ones. The answer is a layered, mixed solution that blends radar with electro-optical and passive RF sensing; electronic attacks up front to disrupt guidance (and datalinks), and relies on mobility and deception. Shoot-and-scoot radars, decoy emitters and dispersed air-base layouts can keep the network alive. The defender’s aim may not perfect protection but enough attrition and confusion to keep own air operations viable and to deny the attacker easy, repeated assaults.

At sea, defensive action is fluid and shaped by the geostrategic and tactical setting. The threat to naval platforms has increased manifold due to constant surveillance from space, air, surface and subsurface. Unmanned surface vessels with warheads, autonomous subsurface craft and high-endurance UAVs have added uncertainty to conventional maritime operations. We have also seen the disruptive potential of explosive USVs in contested littorals and the renewed importance of harbour, strait and convoy defence. Technology, however, works for the defender too as it provides him with wide-area maritime ISR, better acquire-to-shoot chains and the integration of unmanned pickets can extend a fleet’s eyes and buy time. The game is changing; tactics at sea will not be the same. If we envision and adapt quickly, we can get ahead of the curve; if we choose to wait and watch, we will end up chasing the advanced militaries.

New domains complicate matters further. Cyber is constant war by other means. In peacetime it probes; in crisis it surges, aiming at command networks, logistics software, power, fuel and media. Indian cybersecurity agencies face this daily; during Op Sindoor the intensity increased and the targets were of strategic importance. The lesson is to treat cyber as a permanent front.  Adopt zero-trust practices, rotate keys and patches, red-team frequently and rehearse continuity when networks degrade.

Space is likely to see greater militarisation than is admitted in public. There is reason to believe certain militaries hold more capability than they reveal, partly to preserve surprise and partly because technologies are still maturing. As ISR, PNT and communications become more space-dependent, jamming, dazzling and non-kinetic interference will play a larger role. Here too, resilience will come from proliferation and redundancy, multiple constellations, alternative timing sources, hardened ground segments and from recognising that cyber and space are now tightly linked.

What then of robotics? Already a major disruptor, robotics will grow across domains. Sentry and sapper UGVs, cargo drones, autonomous turrets and loitering interceptors are all proliferating. For the defender, there is a real challenge of facing an adversary that is intelligent, fast, tireless and unemotional, whose loss is measured in costs and numbers rather than body bags. The correct response is to use robotics offensively and defensively while building safeguards against spoofing and failure. Human judgement should stay in or above the loop where it matters, but the tempo must shift to match the machine.

In sum, the purpose of defence is no longer only to deny a breach at the front but to preserve combat power, protect depth and impose costs until counter-strokes are possible. That requires a shift from static lines to living systems; systems that hide their vitals, move before they are mapped, deceive sensors as a matter of habit, and repair faster than they are damaged. It also requires political clarity; if depth is at risk from Day 1, then critical civillian infrastructure must be prioritised alongside purely military targets, and national logistics must be prepared to operate under constant harassment.

The defender today must be prepared to make conceptual changes and trade some concrete for cognition, electronic warfare, counter-UAS, decoys, dispersion and rapid repair & maintenance, in order to crack the defender’s dilemma.