Swiss police officers stand beside of mock gates of the NEAT Gotthard Base Tunnel inside the event hall for the upcoming opening ceremony near the town of Erstfeld, Switzerland May 31, 2016. The celebrations of the opening of the Gotthard Base Tunnel will start on June 1, 2016. With a length of 57 km (35 miles) crossing the Alps, the Gotthard Base tunnel is the world's longest train tunnel. (Photo by Arnd Wiegmann/Reuters)

Damaged train coaches at the site of a train accident, 180 kilometers from Bhopal near Harda district of Mahdya Pradesh, India, 05 August 2015. At least 25 people died when two passenger trains derailed in central India after heavy monsoon rains flooded railway tracks, officials said. Ten coaches from the trains toppled while approaching a small bridge just before midnight. (Photo by Sanjeev Gupta/EPA)

Migrants with a stick, stones and knife fight with each other after a brawl erupted over a place in an overcrowded train heading to the Serbian border at the train station in Gevgelija, The Former Yugoslav Republic of Macedonia, 14 August 2015. The number of migrants passing through Macedonia increases day by day, local sources said. From the beginning of the year to mid-June 2015, nearly 160,000 migrants landed in the southern European countries, mainly Greece and Italy, on their way to wealthier countries in Western and Northern Europe, according to estimates by the International Organization for Migration (IOM). (Photo by Georgi Licovski/EPA)

A member of the punk group p*ssy Riot is restrained by a member of the Cossack militia in Sochi, Russia, on Wednesday, February 19, 2014. Cossack militia attacked the p*ssy Riot punk group with horsewhips on Wednesday as the group tried to perform under a sign advertising the Sochi Olympics. The group had gathered to perform in a downtown Sochi restaurant, about 30km (21miles) from where the Winter Olympics are being held.They left the restaurant wearing bright dresses and ski masks and had only been performing for a few seconds when they were set upon by Cossacks. (Photo by Morry Gash/AP Photo)

Flowers are left at the scene of a hit and run following civil disturbances in the Winson Green area on August 11, 2011 in Birmingham, England. Police are continuing investigations after three people – reportedly trying to protect shops from rioting and looting in Dudley Road – were struck by a car. Police have so far arrested over 1,000 people following rioting which erupted over a four-day period across the UK. (Photo by Jeff J Mitchell/Getty Images)

An RAF Eurofighter EF-2000 Typhoon takes off on March 22, 2011 at the Gioia Del Colle airbase in Italy. After last week's UN resolution which voted for a non-fly zone to be enforced over Libya, sorties have continued to be flown by forces representing the UN coalition from Italian military bases. More than 110 missiles have been fired on pro-Gaddafi strongholds in attempt to knock out the Libyan leaders defences.

A 2S5 Giatsint self- propelled gun fires during tactical exercises held by artillery detachments of the Russian Eastern Military District' s 5th Army at the Sergeyevsky training ground in Primorye Territory, Russia on March 21, 2017. Over 2500 servicemen practice combat skills received in 2017 winter training exercises. (Photo by Yuri Smityuk/TASS)

A United States Air Force (USAF) F-15 fighter jet travels at low altitude through the “Mach Loop” series of valleys near Dolgellau, north Wales on June 26, 2018. The Mach Loop valleys, situated between Dolgellau and Machynlleth, are regularly used by the military for operational low flying training which can take place as low as 76 metres from the nearest terrain. The USAF regularly use the loop to practice low-altitude flight, which confuses radar systems. (Photo by Oli Scarff/AFP Photo)