Portuguese paratroopers test their equipment in preparation for a high-altitude low-opening jump during exercise Real Thaw 16 in Beja, Portugal, Feb. 24, 2016. The paratroopers jumped from approximately 18,000 feet to test their HALO jump capabilities. (U.S. Air Force photo/Senior Airman Jonathan Stefanko)

Sgt. Carlos Basilio, Portuguese paratrooper, adjusts his oxygen mask in preparation for a free-fall jump during exercise Real Thaw 16 in Beja, Portugal, Feb. 24, 2016. The paratroopers jumped from approximately 18,000 feet to test their high-altitude free-fall capabilities. (U.S. Air Force photo/Senior Airman Jonathan Stefanko)

Lt. Andre Novais, Portuguese paratrooper, tests his oxygen mask in preparation for a free-fall jump during exercise Real Thaw 16 in Beja, Portugal, Feb. 24, 2016. The paratroopers jumped from approximately 18,000 feet to test their high-altitude free-fall capabilities. (U.S. Air Force photo/Senior Airman Jonathan Stefanko)

Patches of a Portuguese paratrooper are worn as he prepares for a high-altitude low-opening jump during exercise Real Thaw 16 in Beja, Portugal, Feb. 24, 2016. The paratroopers jumped from approximately 18,000 feet and worked with foreign pathfinders who operated the drop zone. (U.S. Air Force photo/Senior Airman Jonathan Stefanko)

A Portuguese paratrooper descends after performing a high-altitude low-opening jump during exercise Real Thaw 16 in Beja, Portugal, Feb. 24, 2016. The paratroopers jumped from approximately 18,000 feet and worked with foreign pathfinders who operated the drop zone. (U.S. Air Force photo/Senior Airman Jonathan Stefanko)