The first successful British nimble tank used in World War 1 was the Mark I. It was developed in 1916 and saw action for the first time in 1917 during the Battle of the Somme. The Mark I was a heavy tank that weighed 28 tons and was armed with two 6-pounder guns and four machine guns. It could move at a top speed of 4.7 miles per hour and had a crew of eight. The Mark I was successful in breaking through enemy lines and proved to be a valuable asset to the British army.