I have learned a great deal from The Custodian
's superb write-ups on the tank
But he does not mention this small tidbit: the main person responsible for the early development of the tank was none other than Winston Churchill, who served as First Lord of the British Admiralty from 1911-1915. Churchill, an authentic geek with low grades in school, turned out to be a brilliant military planner and leader from a surprisingly young age, and recklessly brave under fire. The First World War began under his tenure, and he was active in military planning once it became clear that Germany would likely invade Belgium, as indeed it did on 4 August, 1914.
The situation rapidly became that of trench warfare. On 5 January, 1915, Churchill proposed to "fit up a number of steam tractors with small armoured shelters, in which men and machine guns could be placed, which would be bullet-proof." The idea met with much skepticism and ridicule at first; the tank was widely known in its early days as "Winston's Folly", even within the Admiralty. The name "tank" was proposed in keeping with the plan to pretend the British were actually building water-carriers to aid the Russians.
Armoring of ships, land fortifications, as well as trains and other vehicles was, of course, nothing new in warfare, but the idea of an armored, treaded land vehicle with guns attached definitely was. William Manchester, in his superb biography, traces Churchill's inspiration to a moment on January 3, 1911, during the "Seige of Sidney Street", an armed standoff between London police and a group of Latvian anarchists. As Home Secretary at the time, Churchill was responsible for calling in troops to replace the police, and he took the highly unconventional step of rushing off to Sidney Street to see the situation in person. Since the police could not get close to the building the gang was hiding in, Churchill had the idea of trying to find a large piece of steel that could be used as a shield - the police would climb the building's staircase protected by the shield, shooting as they went.
Shields are a very ancient tool of war, but Manchester believes Churchill's invention of the tank was in part a development of his attempt to use steel shields to approach the Sidney Street gang.