The Solar Impulse 2 airplane, flown by test pilot Markus Scherdel, flies off the coast of Oahu during a test flight from Kalaealoa Airfield in Kapolei, Hawaii, March 3, 2016. The solar-powered plane is ready to continue its revolutionary voyage around the world. After the craft was grounded in Hawaii last July due to overheated batteries, it was repaired and upgraded, and a recent initial test flight proved successful. (Photo by Eugene Tanner/Reuters)

A German special anti-tank gun is ready to fire during the army maneuvers in Silesia, Poland, on September 22, 1928. (Photo by AP Photo)

A U.S. Army soldier with the 10th Special Forces Group and his military working dog jump off the ramp of a CH-47 Chinook helicopter from the 160th Special Operations Aviation Regiment during water training over the Gulf of Mexico as part of exercise Emerald Warrior 2011 on March 1, 2011. (Photo by Tech. Sgt. Manuel J. Martinez/U.S. Air Force)

Indian underprivileged and specially abled grooms and brides in traditional marriage attire arrives to take part in a mass marriage ceremony in Mumbai, India, 29 May 2016. Around 51 couples got married during the ceremony which was organized by Narayan Seva Sansthan, for the underprivileged and specially abled people. From this 51 couples, both the partners are physically disabled in 22 couples, one partner is physically disabled in seven couples and 22 couples are from underprivileged circumstances. (Photo by Divyakant Solanki/EPA)

Hotel staff practice self-defence skills after a training session given by team member of Special Weapons and Tactics (SWAT) team, in Hangzhou, Zhejiang province, April 7, 2016. (Photo by Reuters/Stringer)

Arctic wolves in their new enclosure in the wildlife park in Hanau, Germany, 10 February 2015. The pack is one of the park's main attractions, which specializes in local and European breeds. (Photo by Boris Roessler/EPA)

Italian disabled dancer Simona Atzori (top) performs, before a special audience with disabled athletes led by Pope Francis, in Paul VI hall at the Vatican October 4, 2014. (Photo by Tony Gentile/Reuters)

A Palestinian girl with her body painted by special effects makeup artist Alaa Abu Mustafa, 20, sits on a boat in the southern Gaza Strip, March 22, 2018. (Photo by Ibraheem Abu Mustafa/Reuters)