The platoon was, an American military official would assert years later, “raggedy.”

On their tiny, remote base, in a restive sector of eastern Afghanistan at an increasingly violent time of the war, they were known to wear bandannas and cutoff T-shirts. Their crude observation post was inadequately secured, a military review later found. Their first platoon leader, and then their first platoon sergeant, were replaced relatively early in the deployment because of problems.

But the unit — Second Platoon, Blackfoot Company in the First Battalion, 501st Regiment — might well have remained indistinguishable from scores of other Army platoons in Afghanistan had it not been for one salient fact: This was the team from which Sgt. Bowe Bergdahl disappeared on June 30, 2009.

In the years since Sergeant Bergdahl’s capture by the Taliban, and even more since his release last week in a contentious prisoner exchange for five Taliban fighters, much has been written suggesting that he was a misfit soldier in something of a misfit platoon that stumbled through its first months in Afghanistan and might have made it too easy for him to walk away, as his fellow soldiers say he did.

Indeed, an internal Army investigation into the episode concluded that the platoon suffered from lapses in discipline and security in the period before Sergeant Bergdahl — a private first class at the time who was promoted while in captivity — disappeared into Paktika Province, two officials briefed on the report said.