The Pentagon's restructuring of aviation units in Germany is stoking concerns that the dwindling U.S. presence in Europe is too weak to deter future Russian aggression.

The Defense Department announced April 29 that it is restructuring the 12th Combat Aviation Brigade and subordinate units in Illesheim, Ansbach, Wiesbaden and Stuttgart, Germany, as part of the Army's Aviation Restructuring Initiative in Europe.

The move will result in the reduction of approximately 1,900 U.S. military positions in Germany, according to a recent Army announcement.

Critics have worried that Russian President Vladimir Putin will see the restructuring as another example of how the U.S. presence in Europe has shrunk over the past decade.

"Since the end of the Cold War, U.S. policy toward Russia was based on a bipartisan assumption that the Russian government sought to integrate peacefully into the international order in Europe and to forge a constructive relationship with the United States. ... Today, Russia maintains sizable numbers of artillery pieces and multiple rocket launchers on the territory of Ukraine in violation of the February cease-fire agreement," Senate Armed Services Chairman Sen. John McCain, R-Ariz., said at an April 30 hearing.

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"Yet as Russia builds up, America draws down. The Obama administration eliminated two heavy brigades stationed in Europe in 2012. Yesterday, the Army announced the departure of 24 Apache helicopters and 30 Black Hawk helicopters from Germany."

Air Force Gen. Philip Breedlove, NATO's supreme commander, told McCain that one of his main concerns is that Russian forces are using the recent lull in action in Ukraine to reset and train for future expansion.

"What we see suggests growing Russian capabilities, significant military modernization and an ambitious strategic intent," Breedlove said, describing Putin as a leader who exploits weaknesses and responds only to strength.

"We must strengthen our deterrence in order to manage his opportunist's confidence."

A key aspect of the restructuring of the 12th CAB is the U.S. Army's commitment to provide a persistent, full-time rotational presence in the region, according to Army officials. Rotational forces are critical to the DoD's ability to project power and operate the force globally -- deployed and employed today throughout Europe, the Middle East, Africa and the Pacific.

Breedlove highlighted Operation Atlantic Resolve -- an effort that has involved air, land and special operations forces out of U.S. European Command, "maintaining a presence in all three of our NATO allies in the Baltics -- Poland, Poland and Bulgaria -- providing capabilities such as airborne, armor, mobile infantry, light fighters, strike fighters, advanced air and maritime presence."

Despite the downsizing of U.S. forces in Europe, the remaining presence is still an important deterrent capability, Breedlove said.

"It was our permanent presence in Europe that gave EUCOM the ability to respond immediately after Russian troops illegally occupied Crimea," he said. "Soldiers from the 173rd Airborne Brigade in Germany deployed to the Baltic States within 96 hours of receiving their mission."

Similarly, American F-15s began flying missions out of Poland within 18 hours of the initial alert, Breedlove said.

McCain continues to maintain that the U.S. needs to refocus its efforts in Europe.

"In response to the broader challenge that Russia poses to security in Europe, it is not that the United States and NATO have done nothing: We have created a modest rapid reaction force; increased air policing and sea patrols; expanded training and exercises; and deployed small numbers of additional forces to Estonia, Latvia, Lithuania and Poland," McCain said. "The problem is, the actions we have taken seem inadequate to the scope, scale and seriousness of the challenges we face.

"None of us want a return to the Cold War. But we need to face the reality that we are dealing with a Russian ruler who wants exactly that."

Part of the aviation restructure involves the Army providing a rotational presence consisting of units from an assault helicopter battalion, two medical-evacuation teams, and an air traffic service company to complement the 12th Combat Aviation Brigade, the Army release states.

The rotational force will be located in the Ansbach area with possible short deployments to Eastern Europe in support of training and exercises supporting Operation Atlantic Resolve. These units will rotate for nine months with no gap between rotations, according to the release.

"Rotational presence is not a substitute for permanent-forward presence, but a fully funded rotational presence can play an important role in helping meet the requirements in our theater," Breedlove said.

-- Matthew Cox can be reached at Matthew.Cox@military.com.