Seven months ago 500lb bombs were tearing into Taliban positions outside Sangin district centre in Helmand province as the US Marines here launched an aggressive and costly campaign against Taliban insurgents. What was already Afghanistan's bloodiest district for foreign troops quickly became more so.

The infusion of troops, including US Marines, was part of President Obama's surge and despite widespread suspicion of Nato's spin, it genuinely seems that their arrival had an impact, especially in Helmand and neighbouring Kandahar – although neither province is yet safe, nor going to be in the immediate future. The Taliban matched Obama's surge with their own escalation, knowing full well that tactical defeats matter little, provided they can simply hang-on under the drawdown.

But the gun battles and roadside blasts that once took place in Sangin's heart have migrated to its fringes – and it's hard to see that as anything but a vindication of the Marines' aggressive tactics. Yesterday there was barely a single explosion within earshot of the Marines' main base.

That's not because the fighting's over. First Battalion Fifth Marines have been taking heavy casualties and they're angry and hurting.

There's a daily traffic of dead and wounded to battalion medics, and there are gut-wrenching stories of self-sacrifice, bad luck and suffering. Some say the level of violence in parts of Sangin compares unfavourably with darker episodes from the Iraq war. All of this, though, is happening away from the population hub deemed crucial in counter-insurgency doctrine.

In some eyes that's a definite achievement. "People are not happy with the district chief and the police, but people are very happy with the Afghan National Army and the American Marine group," one local elder says, unprompted, by phone.

"If the American Marines leave Sangin district, then it will be like before, when the British were here, and the Taliban will capture most of the district. Without the American Marines, I don't think any foreign troops could bring the same security."

At the same time as the Marines have pushed deep into what was until recently uncontested Taliban territory, a tentative peace accord struck at the start of the year is holding, at least to the extent that it still exists, however shakily. That's important because even the Marines recognise their firepower may indeed be overwhelming, but can never be conclusive.

There's a poignancy to the fact that, just as headway is finally being made in one of Afghanistan's most notoriously difficult districts, the benchmarks have moved and that's no longer enough.

Instead, the Marines are in a race against time to train up Afghan security forces and establish political pacts that are strong enough to weather Taliban counter-punching. The sooner they're in place, the less bloodshed there will have to be.

Few will be sad to leave. "Most Marines are Republicans," says one officer. "But [even] they think it's enough. Time to hand over to the Afghan police and Army.

"They're a rough bunch of guys," he says, trailing off. But they'll have to do.