More than 2,300 soldiers from three major Army units will deploy to Afghanistan this spring and summer, officials have announced.

The deployments are part of the regular rotation of forces to Afghanistan, where the mission in January transitioned to a train-and-advise mission called Resolute Support.

The deploying units are:

7th Infantry Division headquarters. About 60 soldiers from the unit at Joint Base Lewis-McChord, Washington, will deploy in the summer. They will be led by Brig. Gen. Paul Bontrager, the division's deputy commanding general for support, and they will be responsible for Train, Advise and Assist Command-South.

They will replace soldiers from 1st Cavalry Division. The soldiers are preparing for up to a 12-month deployment, said Maj. Jason Waggoner, a spokesman for the division.

This will be the first deployment for the 7th Infantry Division headquarters since it was reactivated in 2012, and its first combat deployment since Operation Just Cause in 1989, Waggoner said. Originally reactivated to provide training and readiness support to brigades on Joint Base Lewis-McChord, the 7th Infantry Division headquarters was recently reorganized into a deployable unit.

The move comes as almost all of the Army's 10 active-duty division headquarters are committed around the world conducting new missions — in Iraq, Europe and West Africa, for example, as well as enduring ones, such as in Afghanistan and the Pacific.

2nd Brigade Combat Team, 10th Mountain Division. About 1,660 soldiers from the brigade, based at Fort Drum New York, will deploy in the spring and summer.

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"Our team, including both our soldiers and families, is the right organization to take on this mission," said Col. David Doyle, the brigade commander, in a statement.

The soldiers will serve on advisory teams, conduct security operations, and support the TAAC-South staff, said Capt. Jennifer Menard, a spokeswoman for the brigade.

The soldiers are expected to be deployed for about nine months, she said.

101st Combat Aviation Brigade, 101st Airborne Division. About 700 soldiers from the brigade are scheduled to deploy in the spring.

The Fort Campbell, Kentucky-based soldiers are expected to deploy for up to nine months.

There are about 10,000 U.S. troops in Afghanistan; about 8,500 of them are soldiers.

Current plans call for that number to drop to about 5,000 in 2016, but the top commander in Afghanistan, Gen. John Campbell, testified on Capitol Hill earlier this month that he wants "greater flexibility" to potentially keep more troops in-country.

Campbell said his views are influenced in part by Afghan President Ashraf Ghani's request for more U.S. support for Afghan forces in areas such as logistics, intelligence and air support.

"I think I provide some options, both for President Ghani and for my senior leadership here, to take a look at what would allow us the flexibility to continue to get after the [train-advise-and-assist] mission and the [counterterrorism] mission," Campbell said during his testimony.