An army unit probably wouldn't use a guided missile to try to kill a single enemy soldier. The missile may cost hundreds of thousands of dollars, so it would be in limited supply and reserved for much more important targets.
Actually, that was then. Now in Ukraine a guided missile may indeed be aimed at just one soldier. We'd recognise the weapon as a drone, but functionally it's a guided weapon with a revolutionary characteristic: by military standards, it's incredibly cheap.
That cheapness is upending warfare. For a few decades we've expected a big change in military affairs, one in which big, costly and scarce weapons would be challenged by things that would be small, cheap and numerous. In the Middle East and especially in Ukraine, the revolution is upon us.
Drones that return for reuse are cheap, too. They're doing the work of crewed aircraft costing 10 or even 10,000 times as much and doing it without risking the lives of anyone aboard.
So these miniature missiles and attack and reconnaissance aircraft are suddenly abundant in warfare. Some are small aeroplanes; others are little helicopters with four or more rotors for lift. In a wide variety of sizes, they're swarming over the battlefield in Ukraine, multiplying the risks faced by valuable targets such as armoured vehicles, trucks, command posts, artillery, air-defence batteries and ammunition depots.
Because they're cheap and, by the way, easy to use, little drones are weapons for terrorists, too.
This is a massive new challenge for armies. We don't have much insight into what, if anything, the Australian Army and Department of Defence are doing about it.
Companies around the world, including Electro Optic Systems in Canberra, are rushing to come up with better ways of shooting down drones. The great problem is that the traditional methods of destroying aircraft cost more than many of the drones do. So these firms, among which EOS is a leader, are particularly working on weapons that can hit at extremely low cost.
For example, since Israeli forces entered Gaza last month, drones apparently launched by Houthi militants in Yemen have flown towards Israel. A US destroyer has been shooting them down but has probably used at least one multi-million-dollar interceptor missile every time. The drones probably cost no more than a few hundred thousand dollars.
Iran, the Houthis' drone supplier, would be well satisfied with the transactions.
On battlefields in Ukraine, a startling development has been the military use of first-person-view drones - miniature multi-rotor helicopters originally conceived for civil purposes. A user with a radio link sees what the drone's camera sees and can use the aircraft to take pictures or just enjoy racing the thing around.
Add an explosive charge to an FPV drone and you have a precision guided missile. An operator may, for example, guide it to hit and blast through the thin top of an infantry fighting vehicle that has nine soldiers inside.
The cost of the IFV might have been tens of millions of dollars. Add to that the loss of the dead or maimed soldiers. The FPV drone probably didn't cost more than $5000, maybe far less, and its operator could have sat safely in a basement many kilometres away.
Formerly the IFV would have been attacked with a rocket-propelled missile costing more than $100,000. The person who fired it needed a direct view of the IFV and was therefore less likely than a drone operator to line up a shot. The shooter was also in some danger when the opportunity arose.
Or a similar missile could have been fired from a $100 million helicopter with two crew members aboard who risked being shot down.
An FPV missile drone is indeed cheap enough to use against a single soldier. In fact, such attacks in Ukraine so far have probably been made mostly because an operator couldn't find a more important target. But it follows that launching kamikaze FPVs specifically to hit individuals would become frequent when supply of the equipment becomes sufficient.
Meanwhile, drones that return for reuse are routinely making bombing attacks against infantry as well as other targets - for example, by dropping grenades into trenches. Formerly, soldiers on the front line who needed an air strike against an enemy position would send a request up the line and hope that a mighty attack helicopter or fighter aircraft would be assigned to the job. Now they can do it themselves.
Drones are roaming over the battlefield in their thousands to find out what's hiding where. Even if they aren't carrying weapons, their reconnaissance pictures can be used to call in strikes by artillery, rockets or other drones.
Armies and their suppliers need to think hard and fast about what to do about all this. One answer is to jam drones' radio links - and that may work, if the jammer is powerful enough, in the right location and transmitting on the right frequency.
Shooting drones down is most desirable, but the enormous difficulty is finding a way of doing that cheaply enough.
For example, Australia is equipping its army with NASAMS anti-aircraft missile batteries, which are undoubtedly good at destroying high-performance jet aircraft and missiles. But the least expensive interceptor missile fired by a NASAMS costs about $600,000. If that's our only way to bring down $5000 drones, then we'll will run out of interceptors long before an opponent runs out of drones.
Military minds are turning back to old-fashion anti-aircraft guns, because bullets are really cheap and small explosive shells may be cheap enough. Ukraine is indeed having success with manually aimed guns against Russia's lumbering long-range drone aeroplanes that are, in effect, propeller-driven cruise missiles.
But reliably shooting down small, zippy and numerous FPVs is harder. It demands a sophisticated weapon that operates very quickly thanks to automation and economises on ammunition thanks to extreme precision in tracking and pointing.
Canberra's EOS says its Slinger anti-drone gun, which has those characteristics, will score a killing shot at an average cost of $50-$1000, depending on which ammunition must be used. So, finally, we see the drone on the wrong end of a cost calculation.
And ammunition expense is removed entirely if an anti-drone weapon is a laser. Many companies are working on such equipment. EOS has developed one that, after pointing, needs only 1-2 seconds to heat up and soften a target's little plastic propellers. They deform and the drone loses control.
EOS is also developing a lower-powered laser weapon that will offer the alternative of neutralising drones by dazzling their cameras.
Still, there's a nagging doubt about any sophisticated anti-drone weapon: since it must cost at least hundreds of thousands of dollars, it is itself a worthwhile target. The enemy could send against it a swarm of drones that are too numerous for it to handle. The gun or laser would work desperately to bring down one little attacker after another, but ultimately they might overwhelm it.
The problem is familiar to naval strategists contemplating ships defending themselves against massed missile attack.
EOS's answer is to deploy several anti-drone weapons together for overlapping coverage. They could bring down tens of drones per minute, a spokesperson says. Still, more guns or lasers implies more cost, and the other side could respond with yet more drones.
Maybe the addition of jamming and dazzling would even up the balance. Also, drones might be attacked by other drones, perhaps with dropped nets that cause crashes or simply by ramming.
Where these little aircraft are taking warfare isn't clear. What is clear is that we're in the early stages of a revolution.
- Bradley Perrett is a defence and aerospace journalist