The first tanks were developed during WW1 in response to the horrific trench conditions of the Western Front. Both the Entente and the Central Powers had fought to a stalemate in trenches that were difficult to breach by the opposing side. An early idea came in as early as 1914 when a British Lieutenant Colonel named Ernest Swinton proposed adding extra armor plating to an American artillery tractor that could serve as a linebreaker, but the idea was temporarily set aside until 1915. Meanwhile, the French were attempting to use similar designs so as to traverse and the vast fields of barbed wire setup to limit troop movement.
On February 1915, the First Lord of the Admiralty in the British Navy, Winston Churchill formed the Landship Committee, a collection of automotive specialists and military engineers, to pursue research and development into armored vehicles designed to replace cavalry and break the stalemate at the trenches.
The initial criteria for the armored vehicle were as follows (http://history.co.uk/study-topics/history-of-tanks/tank-origins):
-a traction capable of crossing craters and trenches more than 1 meter wide and 2 meters deep under trench conditions.
-capable of carrying heavy firepower to breach enemy fortifications and trench lines
-armored to be heavily resistant to most conventional weapons.
After several failures and prototypes that never made the production stage, a breakthrough was achieved in the form of “Little Willie” (circa early 1916), the first completed tank prototype in history.
Below is a lecture by the Tank Museum’s Historian, David Fletcher, regarding the creation of Little Willie