As many as 10,800 U.S. troops — 1,000 more than originally planned — will remain in Afghanistan in the New Year.
They'll also deploy to Iraq, Europe and the Pacific.
The transition from Operation Enduring Freedom to Resolute Support will happen Jan. 1, as the Afghan National Security Forces take full responsibility for security in the country.
The temporary increase in U.S. troops is meant to cover temporary force shortfalls as coalition troops arrive in theater.
The troop drawdown will continue after the first few months of the year, Defense Secretary Chuck Hagel said during a Dec. 6 visit to Afghanistan. The force will drop to 9,800 before eventually shrinking to 5,500 troops by the end of 2015.
The Army will continue deploying soldiers to Europe in 2015 as part of an effort to reassure its partners and allies in the face of Russian intervention and aggression in Ukraine.
Operation Atlantic Resolve, which was launched in 2014, is meant to reassure Eastern European NATO members that the alliance will defend them if needed. Officials have said the mission is expected to continue for the foreseeable future.
In 2015, the Army will deploy about 100 soldiers from the 4th Infantry Division headquarters to support Atlantic Resolve. Once overseas, the soldiers will provide command and control for Army forces participating in the mission. They also will train alongside NATO allies and partner nations in the region to build interoperability, partner capacity and relationships.
The 4th Infantry Division headquarters, of Fort Carson, Colorado, is regionally aligned with European Command, and it is the first division-level headquarters to deploy to Europe as part of the Army's regionally-aligned forces concept.
In the New Year, soldiers from the 2nd Cavalry Regiment, of Vilseck, Germany, will participate in Atlantic Resolve in Estonia, Latvia, Lithuania and Poland. They are the third rotation of troops to do so.
The Army also plans to add at least 100 fighting vehicles to Europe by the end of 2015. This equipment would be prepositioned in the region for use by rotational units or for contingency purposes, officials said.
Also on tap for 2015 is a quick-reaction force for the region. NATO leaders decided to stand up the force of 4,000 to 5,000 troops during their September summit in Wales, and the intent is for the force to be able to respond to a crisis in Eastern Europe within two or three days.
The goal is for the force to reach initial operating capability in 2015, and while the makeup of this force is still being worked out, Army leaders have said they expect the U.S. military to have a part in it.
The fight against the Islamic State group means more soldiers will deploy to Iraq in 2015.
Operation Inherent Resolve will grow in coming months, with troop levels expected to almost double from the 1,600 in country now to about 3,100.
President Obama in November authorized an additional 1,500 troops to deploy to Iraq to help advise, assist and train Iraqi Security Forces.
About 1,000 of those troops will be paratroopers from 3rd Brigade Combat Team, 82nd Airborne Division. They will deploy in late January for nine months. Also going are about 300 troops, most of them enablers, from the different services.
In addition, another 250 paratroopers from 3rd BCT, 82nd Airborne Division's 1st Battalion, 505th Parachute Infantry Regiment are expected to deploy in late December for a nine-month tour. These soldiers' deployment is not part of the troop increase.
They will join the 1st Infantry Division headquarters, which took command in theater on Oct. 31.
These troops fall under the command of Lt. Gen. James Terry, commander of Combined Joint Task Force-Operation Inherent Resolve and Army Central.
Following the success of its first Pacific Pathway, the Army will run at least two more in 2015. A third Pathway for the year is pending final approval.
The Pacific Pathways program deploys soldiers for three or four months at a time to engage in a series of exercises and training events with partner militaries.
This year, the first Pathway will involve soldiers from 2nd Stryker Brigade Combat Team, 25th Infantry Division, out of Hawaii. They will go to Thailand, South Korea and the Philippines.
The second Pathway will feature soldiers from the 25th Infantry Division's 3rd BCT, also stationed in Hawaii. Those soldiers will go to Australia, Indonesia and Malaysia.
For both Pathways, soldiers will have time in between exercises to conduct military-to-military engagements and participate in cultural events with their hosts.
The three- to four-month rotations are part of the Army's contribution to the U.S. rebalance to the Asia-Pacific region. It also lines up with the Army's regionally aligned forces concept, which aims to commit troops to a specific region of the world to support the geographic combatant commanders.
After almost 50 years in South Korea, the Army will deactivate in 2015 the 2nd Infantry Division's 1st Armored Brigade Combat Team. The Iron Brigade, which has its headquarters at Camp Hovey, South Korea, will be replaced by a rotational brigade combat team from the U.S.
The first rotational brigade to go is 2nd BCT, 1st Cavalry Division, of Fort Hood, Texas, and the 4,600 soldiers are slated to deploy in June.
The 1st BCT, 2nd Infantry Division, has had its headquarters in South Korea since July 1965, training and working alongside its South Korean partners, according to 8th Army. Soldiers who fill the brigade's ranks are deployed to Korea on individual tours.
The plan is to rotate one BCT at a time into South Korea "like we've done in Iraq and Afghanistan for the last 13 years," Army Chief of Staff Gen. Ray Odierno has said. "There'll always be a brigade in Korea, but they'll rotate from the United States."
The Army tested its rotational model with battalion-sized units, beginning last fall when 4th Squadron, 6th Cavalry Regiment, from Joint Base Lewis-McChord, Washington, was sent there for a nine-month tour.
In February, the Army deployed 1st Battalion, 12th Cavalry Regiment, to Korea. The combined-arms battalion from Fort Hood deployed with M1A2 Abrams tanks and Bradley Fighting Vehicles. They were replaced in October by about 800 soldiers from 3rd Battalion, 8th Cavalry Regiment, also from the 1st Cavalry Division.
Officials have said rotating whole units — instead of deploying soldiers on individual tours — will result in formations that are more ready and trained to higher levels.
The Army has about 19,000 soldiers stationed in South Korea.