Željava Air Base, situated on the border between Croatia and Bosnia and Herzegovina under Plješevica Mountain, near the city of Bihać, Bosnia, was the largest underground airport and military air base in the former Yugoslavia, and one of the largest in Europe. (Photo by Thomas Windisch/Exclusivepix Media)

Number 10. BELL H-13 SIOUX was a two-bladed, single engine, light helicopter built by Bell Helicopter. Westland Aircraft manufactured the Sioux under license for the British military as the Sioux AH.1 and HT. In 1947, the United States Air Force ordered the improved Bell Model 47A. Most were designated YR-13 and three winterized versions were designated YR-13A. The United States Army first ordered Bell 47s in 1948 under the designation H-13. These would later receive the name Sioux. The Bell-built H-13 B is seen airborne in this April 29, 1951 photo. The helicopter is equipped with a 173 horsepower engine, cruises at 85 miles per hour, climbs 900 feet in a minute and has a service ceiling of 11,500 feet. (Photo by AP Photo)

Boys dressed in historical uniforms stand before a military parade in Red Square in Moscow November 7, 2014. The parade marked the anniversary of the 1941 parade when Soviet soldiers marched through the Red Square towards the front lines of World War Two. (Photo by Maxim Shemetov/Reuters)

Russian Mi-28N from the Berkuty (Golden Eagles) helicopter display team fly in formation during the “Aviadarts” military aviation competition at the Dubrovichi range near Ryazan, Russia, August 2, 2015. The aircraft started dipping down due to back propeller failure and crashed, killing one of two pilots, according to a Reuters photographer and official representatives of the competition. The aviation contest is part of the International Army Games, which are held in Russia from the 1st till the 15th of August with participants from 17 countries, according to organizers. (Photo by Maxim Shemetov/Reuters)

A Tampa Bay Buccaneers cheerleader, wear a military-inspired outfit as part of the NFL's Salute to Service program, flips her hair during a game between the Buccaneers and San Diego Chargers in Tampa, on November 11, 2012. (Photo by Phelan M. Ebenhack/Associated Press)

The last American military convoy to depart Iraq from the 3rd Brigade, 1st Cavalry Division crosses over the border into Kuwait on December 18, 2011 in Khabari Al Awazeem, Kuwait. (Photo by Mario Tama/Getty Images)

A policeman aims his weapon in Istanbul, Turkey July 16, 2016. Members of Turkey's armed forces said they had taken control of the country Friday as explosions, gunfire and a reported air battle between loyalist forces and coup supporters erupted in the capital. President Erdogan remained defiant and called on people to take to the streets to show support for his embattled government. (Photo by Kemal Aslan/Reuters)