Miniature spring-wound 35-mm film camera in a modified cigarette pack. The Tessina’s small size and quiet operation provided more options for concealment than most commercially available models. (Photo by Central Intelligence Agency)

German field telegraph operators at work in Warsaw. (Photo by Hulton Archive/Getty Images). 1st October 1914

An activist kicks the shields of the military police officers during a demonstration in the military zone of the 27th infantry battalion in Iguala, Guerrero, January 12, 2015. Activists and relatives of the 43 missing trainee teachers from Ayotzinapa's teacher training college broke into the military zone, located less than a mile from where the students went missing, in an attempt to look for the missing students.The remains of only one of the 43 students has been identified so far. (Photo by Jorge Dan Lopez/Reuters)

Russian servicemen display military camouflage equipments during the joint military anti-terrorist command and staff exercise of the armed forces of the Shanghai Cooperation Organization member states Peace Mission-2021 at the Donguz training ground in the Orenburg region, Russia, 23 September 2021. More than 3.4 thousand servicemen from Russia, India, China, Pakistan, Tajikistan, Uzbekistan, Kazakhstan, Kyrgyzstan and more than 600 units of weapons, military and special equipment are involved in the exercise Peace Mission-2021. (Photo by Maxim Shipenkov/EPA/EFE)

A South Korean military vehicle drives past barricades at the military check point, near the Demilitarized zone (DMZ) separating South and North Korea on December 20, 2011 in Paju, South Korea. (Photo by Chung Sung-Jun/Getty Images)

A military cadet gets help from a colleague to adjust her hair before taking part the military parade in Bucharest, Romania, Saturday, December 1, 2018, as thousands turned out Saturday to celebrate 100-years since Romania became a modern-day state, amid concerns about rule of law and the state of democracy. Crowds braved temperatures of minus 5 Celsius (23 Fahrenheit) to watch the military parade of troops, tanks and military vehicles. (Photo by Vadim Ghirda/AP Photo)

Students of the General Yermolov Cadet School take part in combined military training with members of a local youth military patriotic club at a boot camp of the Russkiye Vityazi (Russian Knights) military patriotic club in the village of Sengileyevskoye outside Stavropol, Russia February 8, 2017. (Photo by Eduard Korniyenko/Reuters)

Soldiers of People's Liberation Army (PLA) Lanzhou Military Region jump through a burning obstacle during a training session at a military base in Tianshui, Gansu province, China, January 6, 2016. (Photo by Reuters/Stringer)