On 15 September 1916, at Flers-Courcelette, 49 Mark I tanks rolled into no-man’s land. Most broke down. The ones that kept going shocked the German line and took three villages by lunchtime. Douglas Haig wired London for a thousand more. Building armoured vehicles in volume shaped the next century of wars.

An even bigger shift is under way. The drone has done to the tank what the tank did to the trench. But not only the tank is affected. Drones are changing almost every capability and domain of warfare. Roughly 90 per cent of battlefield casualties in Ukraine now stem from drones. Colonel Al Carns, minister for the armed forces and a former special forces officer himself, notes that one drone now delivers the lethality of 22 artillery shells. Lethality, however, is not the whole story. Conflicts are won by economics, and on this one the ledger is even more stark.

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Consider again the armoured vehicle. A £50,000 strike drone will destroy an Ajax, a Leopard 2 or a Challenger 3, each costing taxpayers between £8 million and £10 million, before support costs are even counted. That ratio is over two hundred to one. The tank, the twentieth-century icon of hard power, is now a very expensive target. We still need armour, but it is no longer decisive.

Air defence runs on the same logic. In March, with the US-Iran-Israel conflict at full pitch, an Iranian Shahed launched from Lebanon struck a hangar at RAF Akrotiri. Ministers praised the RAF crews flying round-the-clock intercepts from the base. Rightly so. The ledger was quieter. Shaheds cost Tehran between £25,000 and £50,000. We shoot them down with air-to-air missiles costing £200,000 to £2 million, fired from Typhoons worth over £100 million each, running at £75,000 an........

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