Who were the three US soldiers killed in Afghanistan?

The bodies of the three US soldiers killed in an apparent insider attack in Afghanistan returned to American soil on Monday.

Their flag-draped caskets were brought off the plane at Dover Air Force Base as Vice President Mike Pence attended, standing with his hand over his heart.

The three men belonged to the 101st Airborne Division and were all in their 20's.

The Pentagon identified them as Sgt. Eric M. Houck, 25, of Baltimore, Maryland; Sgt. William M. Bays, 29, of Barstow, California; and Cpl. Dillon C. Baldridge, 22, of Youngsville, North Carolina.

They were shot during an attack on Saturday when an Afghan army commando opened fire, in what's known as a "green-on-blue" incident, according to US officials. This is when members of the Afghan security forces turn their weapons on US and other NATO soldiers who are training them and fighting along their side.

The Taliban claimed responsibility for the attack saying that an "infiltrator" had joined the Afghan army and attacked the American soldiers, according to its spokesman.

The incident is under investigation.

"I feel betrayed," Chris Baldridge, who was mourning the death of his son, Dillon Baldridge told WTVD. "(Dillon's) over there training people to take care of themselves and then they turn on us."

The attack occurred during a joint US-Afghan military operation in the Nangarhar province, officials said. It was in the Achin District, where US and Afghan troops have been carrying out an offensive against a local affiliate of ISIS, officials said.

Sgt. Eric M. Houck, 25

Houck, of Baltimore, had left for his first overseas deployment and was due to come home next month, his father Mike told CNN affiliate WBAL.

He joined the Army in 2013.

Houck married his high school sweetheart and they had two children, ages 5 and 3. He enlisted as a way to support his family and to serve his country, Houck told the Baltimore Sun.

"He grew up to be a tremendous human being, just a great father, loving son, husband," Mike Houck said of his son. "He was very compassionate, caring, and was concerned about people. He fought for the underdog. He was just a tremendous young man."

"He is a hero," he told the TV station.

The Army posthumously awarded him the Bronze Star, Purple Heart, Combat Action Badge and Army Commendation Medal with a second oak leaf cluster for his end of tour awards.

"Our sincere prayers go to his wife, Samantha, their children, and all of their family and loved ones in this time of grief," Maryland Gov. Larry Hogan posted on Facebook.

The governor said US and Maryland flags would be at half staff when Houck is laid to rest.

Sgt. William M. Bays, 29

Bays hailed from Barstow, California, and joined the Army in 2009.

He was an infantryman in the 101st Airborne Division, based at Fort Campbell, Kentucky. He was also a squad leader, according to the Army.

Bays leaves behind a wife and three children, reported the Stars and Stripes.

The Army posthumously awarded him the Bronze Star Medal, Purple Heart, Combat Infantry Badge and Army Commendation Medal with one oak leaf cluster for his end of tour awards.

Cpl. Dillon C. Baldridge, 22

Baldridge, of Youngsville, North Carolina, was due to return home this summer after deployment.

Family members told CNN affiliate WRAL he went to Afghanistan in October and was set to be back in August.

Baldridge had always dreamed of being a soldier, his father told CNN affiliate WTVD.

"He'd be up at five in the morning watching the Military Channel on TV. What kind of kid does that?" said his father, Chris Baldridge said.

"I was always impressed by Dillon. He was a motivated kid. Whatever he wanted to do, he was going to do it."

Baldridge graduated from Franklinton High School in 2012, said Russell Holloman, the principal.

"He made an early commitment to the military during his high school career and maintained that focus and selfless dedication after graduation," Holloman said in a statement. "Our community has truly lost a hero."

Baldrige joined the Army in 2013 and was assigned a squad leader.

His father told WTVD that Baldridge was a top soldier in his class and turned down an offer to become a Ranger to join his team in its deployment to Afghanistan.

"My chest was just out a little higher that day, beaming with pride," Baldridge told WTVD.

The Army posthumously promoted Baldrige to Sergeant and awarded him the Bronze Star Medal, Purple Heart, Combat Infantry Badge and the Army Commendation Medal with one oak leaf cluster for his end of tour awards.