HUNTSVILLE, Ala. – As the US Army grows its presence and steps up its activities and partnerships in Europe, the service has learned many lessons on navigating border crossings and securing diplomatic clearances across the region.

In fiscal year 2014, the Army processed about 2,000 diplomatic clearances, one for every border crossing, said Maj. Gen. Duane Gamble, commanding general of the 21st Theater Sustainment Command. That number almost tripled in fiscal 2015, with soldiers handling almost 5,700 diplomatic clearances as troops moved and trained in countries such as Poland, Latvia, Estonia, Romania and Bulgaria.

"It frustrates us all that we can't move stuff rapidly across these borders, but they're sovereign borders," Gamble said Wednesday during a meeting here with reporters at the Association of the United States Army Global Force Symposium and Exposition. "The No. 1 friction point is diplomatic clearances."

For example, it takes 15 to 30 days to get clearance to move materiel across the Polish border, he said.

But "the countries are listening," Gamble said, adding that at least one is looking to ease its border restrictions for US troop movements.

The challenge of traveling across Europe, including in convoys of heavy armored vehicles, is an issue senior Army leaders in Europe have grappled with at least since the launch of Operation Atlantic Resolve, which sends soldiers across Eastern Europe to train with and reassure US allies in the face of Russian aggression.

Last year, Lt. Gen. Ben Hodges, commander of US Army Europe, said the highest demand for his soldiers seems to be for movement control teams.

"We have very few of them, and in order to ensure freedom of movement, all these convoys and in-and-out rotations, we have taken out of hide movement control teams and put them in each of the embassies."

In March 2015, US Army Europe launched Operation Dragoon Ride, an unprecedented exercise that "road marched" columns of Stryker vehicles across Eastern Europe.

Dragoon Ride was designed to reassure America's allies, but it also tested the Army's ability to freely move from one country to another, Hodges said at the time.

"President Putin exercises freedom of movement all the time. He moves troops and stuff around Russia whenever he wants to," Hodges has said. "For the alliance, you've got to do that by moving from country to country, and what we've discovered, even though these are all NATO countries and EU countries, each one still has different diplomatic clearance requirements."

Since last spring, the Army has placed soldiers in National Movement Control Centers in each of the Eastern European countries, Gamble said. These soldiers specialize in working with their host nation partners on clearances and other movement control issues, he said.

In addition, NATO recently stood up six NATO Force Integration Units, with two more on the way for a total of eight units. Born out of the Wales summit about 18 months ago, these units each have about 40 people, including a major and lieutenant from the US Army. The units – currently in Estonia, Latvia, Poland, Lithuania, Romania and Bulgaria – are designed to be long-term coordination elements to aid with clearances and reception and staging of troops.

"Our National Movement Control Center soldiers are still there, but there's a new node in the network," Gamble said. "This node is not only on the network, but it has authority from the host nation, and it has the authority to coordinate NATO operations."

Spc. Jace Leeth, of 4th Squadron, 2nd Cavalry Regiment, throws a Polish practice grenade Sept. 15, 2015, at the Drawsko Pomorskie Training Area in Poland. The soldiers are in Poland as part of Operation Atlantic Resolve.

Photo Credit: Spc. Marcus Floyd/Army

As these NFIUs mature, the US Army will continue to place two officers in each unit to help.

"We have two years of experience moving forces in and out of those countries," Gamble said. "We know where the friction is, what the bureaucracy requires."

Other transportation and movement issues the Army is working through include the challenge of moving heavy vehicles across Europe, Gamble said.

The axle weight on the Army's Heavy Equipment Transporter, or HET, exceeds European Union road limitations, he said.

"When we put an M1 Abrams tank on a US Army HET, we can't drive it anywhere in Europe except for the Baltic countries," Gamble said. "We're limited in our freedom of movement currently to move in tanks [and they] have to go by rail."

This leads to other challenges such as the 45-day lag time required to order rail from a private company in Germany.

The Army also lacks information about roadways and systems in Eastern Europe, Gamble said.

"During the Cold War, we reconned every route and marked them," he said. "There were signs that said 'this bridge can take XX weight.' In Eastern Europe, that wasn't the case."

To fix that lack of information, military police and engineer soldiers from the 21st TSC have conducted route reconnaissance on more than 15,000 kilometers of roads in Eastern Europe and logged all of that information in a single database.

"The US is very well practiced in moving across the countries, but in the long run, the NFIUs will help the US with mobility," Gamble said.

Maj. Scotty Autin, operations officer for the 173rd Airborne Brigade Special Troops Battalion, ushers in a Stryker-armored vehicle convoy, from 2nd Squadron, 2nd Cavalry Regiment, as part of a forward passage of line movement at Smardan Training Area, Romania, March 24, 2015.

Photo Credit: Staff Sgt. Opal Vaughn/Army

In addition to ensuring freedom of movement, the 21st TSC, which is tasked with sustaining US European Command and US Africa Command by opening ports and lines of communication and sustaining the theater with everything from laundry and showers to supplies and medical, is staying busy across Europe.

One of its priorities is preparing for the pending upgrade of the 2nd Cavalry Regiment's Stryker vehicles.

The Army approved upgrades for 81 vehicles in response to urgent requests from the Germany-based brigade to replace its .50-caliber machine guns with a 30mm gun and turret amid fears the eight-wheel vehicles were being outgunned by their Russian counterparts.

Plans call for the new vehicles to begin fielding in fiscal 2018.

The upgrade "is something everybody is looking forward to," Gamble said.

"Anything to make our assigned forces more lethal is absolutely the right thing to do," he said. "The Strykers give us a level of mobility that we don't have in our mechanized forces in Europe."

As 21st TSC prepares for the upgrades, it is working to make sure there is enough ammunition for training and combat loads, Gamble said. The command also is making sure the Stryker maintainers are ready for potential issues that may arise by the added weight on the new vehicles.

This includes sending welders for additional training on hull repair, he said.

"There'll be more weight on the older Stryker hulls, and we are already taking measures now … to establish some capability organic in Europe to do hull repair on Strykers," Gamble said.

Michelle Tan is the editor of Army Times and Air Force Times. She has covered the military for Military Times since 2005, and has embedded with U.S. troops in Iraq, Afghanistan, Kuwait, Haiti, Gabon and the Horn of Africa.