Iron monsters: Developed in secret by the Admiralty under Winston Churchill, tanks, or 'landships' as they were originally known, first saw action on the Somme in September  1916. This one, named  Iron Duke, is clanking through the city of Arras to spearhead the British offensive there in April 1917. They were hellishly hot for their crews and liable to break down, but tanks helped end the deadlock  of the trenches in 1918