On 15 September 1916, the first tanks rolled into battle at the Somme. Since then, they have become an important weapon for armies across the globe, used to devastating effect in the Second World War, the Vietnam War, the Iraq War and countless other conflicts. We are looking back at the history of armored warfare over the last 100 years, kicking off our commemorations with a blog from David Fletcher, author of the recently published British Battle Tanks: World War I to 1939.