"We had a platoon full of guys that were on a lighter side of life (who) liked to joke around," retired Sgt. 1st Class Jonathan Hill recalled. "And Carter never really got involved ... he thought it was immature.
"Carter really didn't make friends with a lot of guys, and he struggled with it."
A little over a year after he enlisted, Carter and his platoon were deployed to eastern Afghanistan in May 2009.
Despite his aloofness toward his fellow soldiers, Carter would find himself in a situation where he didn't think twice to risk his life for those men whose jokes he once found childish.
Combat Outpost Keating had been built in Nuristan province in 2006 as part of the effort by NATO-led forces to build partnerships with local Afghans, and try to stop insurgents from trickling over in nearby Pakistan.
The camp had experienced ups and downs since that time and by 2008, the cavalry commanders in charge of the outpost thought it made sense to shut it down.
Yet there were other factors at play.
Afghanistan's President Hamid Karzai was in the middle of his re-election campaign in fall 2009, and abandoning Combat Outpost Keating might have been seen as a lack of American support.
So, despite numerous warnings, Gen. Stanley McChrystal -- then commander of all U.S. troops in Afghanistan -- kept the outpost open.
After Karzai's victory and the end of a military operation that freed some key assets, the military leadership approved a plan to abandon the outpost and the troops stationed there were to start packing up on Oct. 4, 2009.
That never happened.
Instead, a day before their planned departure, an assault was unleashed on the outpost that culminated in what has now been described as one of the most intense battles of the entire war in Afghanistan.
The first shots rang out just a few minutes before 6 a.m. The rumors that the soldiers had heard for months were coming true. Carter said he had often imagined that day.
"I was like, 'Well, if it's my time to go, how am I going out?' " he said.
The Taliban had studied how the Americans responded to previous attacks, and they knew the outpost relied heavily on its mortars.
So they made the big guns their first target.
"When the enemy weren't shooting at us, they were shooting at the weapons," Carter said. "So they were disabling the weapons."
The insurgent fire killed Pfc. Kevin Thomson as he raced to his post. Sgt. Josh Kirk was killed while returning fire.
"You could hear the rounds coming in from every direction," said platoon Sgt. Jon Hill.