Two dummy tanks being pushed along a road by German soldiers. (Photo by Hulton Archive/Getty Images). Circa 1925

These black-and-white photos are taken from the new book “Armoured Warfare in the First World War 1916 – 1918” by Anthony Tucker-Jones and published by Pen & Sword Military. Here: British troops hitch a ride on a Mark IV after the massed tank fleet spearheading attack at Cambrai on November 20, 1917. (Photo by Anthony Tucker-Jones/Mediadrumworld.com)

Team Strong Silvers member Ngai Hin Kwok, 66, works out as teammate Ng Siu Chi, 57, watches at a stadium in Singapore March 15, 2015. Team Strong Silvers, is a group of senior citizens who train in calisthenics. The trio trains individually at least three times a week, and meets up for joint calisthenics at least twice a month. (Photo by Edgar Su/Reuters)

The main entrance and blast door at the nuclear bunker site on the Woodside Road industrial estate on February 4, 2016 in Ballymena, Northern Ireland. The underground shelter has been put up for sale by the offices of the Northern Ireland First and Deputy First Minister. The bunker which was completed in 1990 was built to hold up to 235 people in the event of a nuclear bomb and is complete with kitchen facilities, dormitories and decontamination chambers. The site, one of approximately 1,600 nuclear monitoring posts built in the UK since 1955, is on the housing market with an asking price of £575,000. (Photo by Charles McQuillan/Getty Images)

Three one-month-old lioness cubs are held by a keeper as they take their first outing on February 21, 2010 at the Ramat Gan Safari Park near Tel Aviv, Israel. The still unnamed cubs are the first triplet females to be born at the safari park and officials say their birth will ensure the continuity of the park's pride of lions. (Photo by David Silverman/Getty Images)

Triston surfs a wave as his father, Todd, watches in Morro Bay. “Hes the most coordinated 3-year-old I've ever seen”, says the 35-year-old captain/paramedic with the Morro Bay Fire Department. (Photo by Joe Johnston/The Tribune of San Luis Obispo)

An unknown number of guns are being built with the mechanisms, causing problems for the police and ATF officials. Photo: An ATF agent holds a generic unfinished receiver, back, and one that has been manufactured, front, at an ATF field office in Washington, on May 06, 2014. The ATF is trying to crack down on the trade in the makeshift guns by targeting shops and individuals who offer to turn the unfinished receivers into functional pieces for firearms. (Photo by Bill O'Leary/The Washington Post)