American soldiers with the 173rd Airborne erect a sign marking a break area on April 21, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. Operation Fearless Guardian is a six-month training exercise involving about 300 members of the American 173rd Airborne and about 900 Ukrainian National Guard troops. (Photo by Pete Kiehart/Getty Images)

An American soldier takes notes on basic Ukrainian and Russian words during the first day of Operation Fearless Guardian on April 21, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. (Photo by Pete Kiehart/Getty Images)

A Ukrainian soldier carries a simulated wounded comrade as American soldiers yell instructions in a "Combat Lifesaver Course" during Operation Fearless Guardian on April 22, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. This exercise began with a run, and included American instructors constantly yelling at the trainees to simulate the stress of a battlefield. (Photo by Pete Kiehart/Getty Images)

American and Ukrainian soldiers work to open a gate in an RPG cage, designed to protect against rocket fire, on an armored vehicle during Operation Fearless Guardian on April 22, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. (Photo by Pete Kiehart/Getty Images)

A Ukrainian soldier shakes hands with one of his instructors after taking part in a "Combat Lifesaver Course" during Operation Fearless Guardian on April 22, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. (Photo by Pete Kiehart/Getty Images)

Ukrainian soldiers practice cutting wire in a breaching class during Operation Fearless Guardian on April 22, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. (Photo by Pete Kiehart/Getty Images)

An American instructor, center, conducts an after-action review as an interpreter, right, reacts after a difficult translation following a building-clearing exercise during Operation Fearless Guardian on April 22, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. (Photo by Pete Kiehart/Getty Images)

Ukrainian National Guardsmen practice inserting nasopharyngeal airways after a lecture on the subject by American soldiers during Operation Fearless Guardian on April 21, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. Nasopharyngeal airway, or NPAs, are used to ensure an unconscious patient's airway doesn't become obstructed. (Photo by Pete Kiehart/Getty Images)

A Ukrainian soldier practices firing a GP-25 grenade launcher during Operation Fearless Guardian on April 23, 2015 in at the International Peacekeeping and Security Center near Yavoriv, Ukraine. (Photo by Pete Kiehart/Getty Images)

A Ukrainian soldier treats a simulated wounded comrade as American soldiers look on in a "Combat Lifesaver Course" during Operation Fearless Guardian on April 22, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. (Photo by Pete Kiehart/Getty Images)

An American soldier holds a target used for instructing in aiming vehicle weapons during Operation Fearless Guardian on April 22, 2015 at the International Peacekeeping and Security Center near Yavoriv, Ukraine. (Photo by Pete Kiehart/Getty Images)