ANGIN, Afghanistan—After four bloody and frustrating years trying to secure the most dangerous town in Helmand Province, the British are pulling out with, at best, a draw.

Over the coming months, U.K. forces will leave Sangin and turn it over to the U.S. to finish the job.

Neither British nor U.S. officers describe it this way aloud, but it's hard to avoid the conclusion that U.S. Marines are being sent in to complete what the undermanned British couldn't, in a province once known as Helmandshire for the U.K.'s dominance here.

Although British officers point to incremental security gains, they acknowledge they simply haven't had enough men to oust the hundreds of Taliban fighters who attack from the shadows, litter the landscape with hidden explosives and blend in easily with the locals.

"The concentration of force is something we haven't been able to bring in here," says Royal Marine Maj. Aldeiy Alderson, chief of staff of Combined Force Sangin.

Almost one-third of the 335 British troops killed in Afghanistan since 2001 have died in this single town of 20,000 people.

"Helmandshire is symptomatic of the broader problem in Afghanistan—that we as a coalition haven't had the resources needed to get the job done," says John Nagl, head of the Center for a New American Security, a Washington think tank.

In the past two years, the British fought to a stalemate in Garmsir and Now Zad, only to see larger American forces sent in to clear the towns. U.S. Marines are also taking over Kajaki, site of a key hydropower plant.

Sangin is a test of whether it is possible to reverse the gains the Taliban have made against British forces in Helmand Province. The Americans—the 1,200-strong Third Battalion, Seventh Regiment—have been entering Sangin since July and, fighting alongside 1,200 Royal Marines, appear to be making headway.

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