Last major Helmand handover like no other
The last sizeable British force to be sent to Helmand province in southern Afghanistan begin their mission later as 7th Armoured Brigade - the "Desert Rats" - take over from 1st Mechanized Brigade. The Afghan operation is codenamed Herrick, but Herrick 19 is unlike any that have gone before.
British troops were once in more than 130 bases here, but are now down to five, and that will reduce still further.
They rarely patrol. The formation of the brigade has changed too. The Desert Rats have enough armour and infantry to protect themselves and take the war to the Taliban if need be, but a large part of the force is made up of engineers and logisticians engaged in packing what they can bring back and disposing of what they cannot.
Some of the troops now arriving in Helmand will stay for nine months, but most will leave earlier as the force rapidly scales back from the 5,200 it will be at the end of this year.
The outgoing Brigadier, Rupert Jones, told me that as British troops stepped back security would be sustained.
I asked him for his reaction to President Karzai's comments in a BBC interview that Nato had caused only suffering for Afghanistan.
"You'll forgive me if I don't comment on what the president of this country has said. That is clearly his business. What I would observe is local commanders, local governance leaders here who are hugely grateful.
"They recognise that enormous progress has been made here. They know that is in large part due to ISAF previously."
One of those local governance leaders, the deputy district governor of Nad Ali, Auliya Atrafi, confirmed the brigadier's view with an anecdote.
"Yesterday a police officer came by at sunset. He was having tea with us. He was saying that the day when the Taliban saw the British withdraw, they were dancing in the desert, saying 'Next week we will be having our meal at the district centre.' And it's been quite a while and they haven't been to the district centre."
Progress has come at a cost. I was on the first British patrol onto the streets of Lashkar Gah in January 2006 when soldiers wore soft berets, proudly pointing out how they were going to do things differently as a US patrol passed by in heavily-armoured vehicles.
But the optimism of Corporal Scott Hodgkinson, who told me on the streets back in 2006 "everyone has been really friendly; they're happy to see us, the British", was clearly misplaced.
This week when I went out to see an aid project, I travelled in the sort of heavily-armoured military vehicle the British used to mock.
Before British soldiers were sent down to Helmand, five British soldiers had been killed in the first four years of the Afghan intervention.
However, 439 more have died since the decision to send troops to Helmand was made, when Defence Secretary John Reid said: "We would be happy to leave in three years and without firing a shot."
He meant, of course, that they had been sent to provide support for an aid programme, not to fight a war.
Colonel Henry Worsley, the first commanding officer in those long-ago days of soft-beret patrols told me they wanted to grab development "by the scruff of the neck".
Since then I have been here pretty well every year, and seen just how hard it is to make a difference.
Once I went to see how a programme to encourage women to plant vegetables and keep chickens was going. The plastic sheeting on the greenhouses had gone, no vegetables grew, and the chickens had disappeared, presumably into the pot.
And there was to be a business park, close to Bost airport in Lashkar Gah, designed to encourage food-processing plants for export, with lucrative deals for investors. The money disappeared and the business park was never built.
If you mention it now, there is an embarrassed silence and shuffling of feet among aid officials.
And there is the continued failure to eradicate the opium poppy.
I have been briefed frequently here by earnest agricultural economists on how they were going to provide alternative livelihoods for poppy farmers.
But three times as much opium was produced in Helmand last year as when British troops arrived.
Most of the illegal heroin on sale in Britain comes from poppies grown in Afghanistan.
And yet, despite the cost, the loss of life and the blunders, there has been some genuine progress.
It is hard to knock the enthusiasm of a girl like Raihanna, in her last year at school, speaking good English and now on her way to medical college, something that would not have been possible under the Taliban.
There are functioning courts, and a prison that is far superior to other Afghan facilities.
When I went to see it last year, a woman who had come to visit her son told me, without being asked, that this was a really good jail. Far better, she added, than the one where her other son was being held in Kandahar.
But uncertainty remains over what will happen next as British and other foreign forces disappear from the landscape.
International forces are drawing down and ending the war on a timetable. But Afghanistan has a history of upsetting the best-laid plans.