The conflicts in Iraq and Afghanistan have once more shown us armies fighting new wars with the methods of the old. When I was a soldier doing National Service in the 1950s, I joined an army identical to the one that had fought the Second World War 10 years previously. In new circumstances, however, the old force structure does badly. Hence the British jibe that we lose every battle except the last. Victory is achieved when a new way of fighting has been adopted.
That this moment has now arrived in Afghanistan was signalled earlier this week by the sacking of the top US commander, General David McKiernan. This is the first time since the Korean War, when President Truman dismissed the headstrong General Douglas MacArthur in 1951, that the US government has removed a general while he was on active combat duty.
General McKiernan was an expert in the use of heavy armour. His successor, Lieutenant-General Stanley McChrystal, is a special operations specialist. That is the key difference. Manoeuvering tanks is old style, operating behind enemy lines is new style. Lt-Gen McChrystal recently ran all the commando operations in Iraq. Such capabilities are required by the new US/British approach outlined by John Hutton, the Defence Secretary, when he called recently for a "rebalancing of investment in technology, equipment and people to meet the challenge of irregular warfare".
In the First World War, this turning-point in methods came in 1917 when tanks and aircraft were used in action for the first time. Three years earlier, the French and British armies had confidently taken their horses and sabers up to the front line.
Lt-Gen McChrystal is one of the few warrior-scholars. He has worked at the Council on Foreign Relations, a very prestigious think-tank in New York, as well as spending night after night in Iraq chasing down terrorists. He eats just one meal a day in order to avoid sluggishness and runs to work listening to audio books on his iPod.
He reminds me of the British general, Orde Wingate, a pioneer in special operations, who during the Second World War often wore an alarm clock on his wrist that would go off at times. He also kept a raw onion on a string round his neck in case he required a snack. When the eccentrics come to the fore, we know we have entered a new phase.
The new model of warfare does simultaneously what used to be done serially. High-intensity combat is conducted in parallel with seeking local support and getting on with reconstruction projects. Forces must now combine soldiers, police and civilians with the capacity to undertake various humanitarian and legal activities. There are few set-piece battles. Rather than killing the enemy, it is better to disable him. Only then can he be questioned or released if he wasn't a combatant after all.
The British general Sir Rupert Smith argues that the transparent operation of law, monitored by international observers, will be crucial in the Wars against Terror. He comments: "If we are to operate among the people, we must do so within the law. To do otherwise would be to undermine our own strategic objective, to establish and uphold the law."
Among the many problems ahead for the Nato, three stand out. Naturally there is great emphasis on force protection but this brings with it a difficulty. Force protection is secured by the use of body armour, heavily armoured vehicles and well-protected bases. As Gen Smith has observed: "We fight so as not to lose the force". Nonetheless, this distances military personnel from the very civilians they are seeking to protect. It enhances rather than reduces mutual suspicion.
Moreover, the question of whether there is one theatre of war, Afghanistan and northern Pakistan itself, linked by dangerous border area, or whether these two countries must for military purposes be treated separately, has not been resolved. Last month, Gordon Brown sought to blur the distinction, saying "the greatest international priority is the border areas of Afghanistan and Pakistan. They are the crucible for global terrorism, the breeding ground for international terrorists, and the source of a chain of terror that links the mountains of Afghanistan and Pakistan to the streets of Britain".
The final doubt concerns the Afghanistan as a state. It is shortly to hold its second presidential election. But corruption is unchecked. Discrimination against women receives legislative support and warlords increase their power. At a certain point, moral revulsion could take hold among Nato governments and their electorate. Why should a single soldier of ours die for this, we may well ask one day?