The British deployed the vehicles we know as tanks on September 15, 1916, at the Battle of the Somme, a four-month catastrophe of a fight that left over a million British, French, and German soldiers dead or wounded. It remains one of the deadliest battles in human history. And the tanks weren't impressive, either. The Royal Army's first, the Mark I, was a slow, ungainly, heavily armored thing that bears little resemblance to its descendants.
But tank warfare, like every other sort of war, evolved rapidly. This video, provided by an unverified YouTube channel listed as British Army gives an idea of the rapid pace of advancement. From the lumbering Mark I and its puny 3.7-mile-per-hour top speed, tanks evolved quickly adding speed, armor, and fire power and turning into the weapons we know today.