In concert with NATO allies and partner nations, the U.S. military is in the midst of a massive exercise in Europe designed to practice moving massive troops formations and equipment across the Continent in the event of a Russian invasion.

A total 23 nations are participating in Sabre Guardian, as the exercise is called, during the month of July. The event is meant to be a tremendous show of force by NATO just two months before Russia will hold its own practice run at an offensive on the opposite side of the border in its western military district.

It will also give U.S. commanders on the ground an opportunity to practice moving its chess pieces around the European board now that an armored brigade combat team and significant aviation and missile-defense assets have been committed to the mission of Russian deterrence, according to Lt. Gen. Ben Hodges, commander, U.S. Army Europe.

“In order for it to be a viable option, you have to practice it,” Hodges said during an interview from Bezmer Air Base, Bulgaria, that was broadcast at the Association of the U.S. Army’s Arlington, Va., headquarters. “You have to have the aircraft. You have to have the quality people and go through the training and have the equipment that makes that a viable option for our leaders.”

The exercise is hosted by Hungary, Romania and Bulgaria. The three nations are “all in on this thing,” Hodges said. A total of 23 countries from NATO and outside the alliance are participating in the multi-day exercise.

“These countries are completely committed to participation,” Hodges said. “Host nation support is a very important part of their contribution. It’s not just 2 percent, although that is part of it. It’s host-nation support that is provided for infrastructure, helping us move through towns.”

After Hodges spoke, a flight of Boeing [BA] C-17 Globemasters and Lockheed Martin [LMT] C-130 Hercules aircraft dropped equipment and paratroopers on and around the airfield. The troops landed and simulated capturing the airfield, which will be used the following day to bring in heavier supplies and establish a salient behind enemy lines. U.S. and allied troops also have completed bridging exercises, live-fire drills and maneuver practice with tanks and armored vehicles. 

Russia has proclaimed the NATO exercise a provocation, although it has a huge exercise in the same vein planned for September in the Western military district that borders NATO.

The Russian exercises rotate military districts every year so every four years one is held in its Western district, or Zapad. He said it is “perfectly normal” for the Russians to hold an exercise in 2017.

In some ways Russia uses its exercises in part the same way NATO does, to practice strategic and tactical concepts and “lots of stuff and lots of people long distances,” Hodges said.

“This is no different, but for some reason this year people seem a little more anxious about it than they have in the past,” he said. “There was an exercise before they invaded Georgia in 2008. There was an exercise going on before they invaded Ukraine.”

History suggests Russia also uses its exercises as a type of Trojan Horse and a pretext to invade or interfere on foreign soil. Prior to the invasions of both Georgia in 2008 and Crimea in 2014, Russia launched unannounced military “exercises” to marshal forces under a peaceful pretense, then exploited a perceived conflict to launch an invasion of sovereign territory.

“I don’t think that’s likely to happen, but it has happened and certainly everybody that lives anywhere close to that area, from Finland and Sweden all the way down to Romania believes that it’s possible … that Russia will use this as an opportunity to leave a lot of capability in Belarus,” Hodges said.

Estimates suggest as many as 100,000 Russian personnel will participate in the September exercise, though not all will be in the field, Hodges said. Russia will practice an offensive against NATO as a whole-of-government event with multiple agencies and ministries involved, he said.

“I suspect they are interested in the same thing I am interested in, which is logistics – how do you move a lot of stuff and get it where you need it real fast?” Hodges said. “The number of guys that will have worked up a sweat and got some dirt on their boots and got their weapon dirty in an exercise is going to be way less than 100,000. But depending on where you draw the circle, the number of people participating will be a lot.”

NATO Secretary General Jens Stoltenberg has said that previous experience suggests Russia will not adhere to international norms when it holds the Zapad exercise in September, but that the event has not occurred and therefore Russia should be given the benefit of the doubt.

Hodges said NATO and the U.S. Army in particular are keeping an eye on Russian military activities along the alliance’s eastern flank, but Sabre Guardian is not a provocation or a pretext to war. 

“The posture of allied forces from Estonia down through Bulgaria is normal readiness. We are not looking for a provocative, Sharks vs. Jets out in an alley chest bumping,” he said. “Instead, we’ll be ready.”