One of the most important tasks for British tank building pioneers was sufficient off-road performance for their "land ships". The "Small Willie" tank, built on the Holt tractor chassis, proved incapable of crossing terrain covered in shell craters, let alone wide trenches and ravines. In order for the vehicle to cross them, it needed to have a much longer track support surface.
This is when engineers decided to shape the tank like a parallelogram and wrap it around the top of the hull. This not only increased the length of the tank, but the height of traction, which let the tank cross very tall obstacles. This gave birth to "rhombus tanks", common for British tank builders for some time.
The first experimental "rhombus" was built, and a proving grounds was prepared for trials. In order to maintain secrecy, the military used the land of Lord Salbury's private golf course. All sorts of obstacles were constructed on it: trenches, craters, wire. Initial mobility trials proved promising.
The positive effect of good mobility was balanced by its downside: the rhombus-shaped tank had to mount its armament in sponsons, which removed the capability of a 360 degree firing arc.
The new tank had several nicknames: "Mother", "Centipede", "Wilson's vehicle". The most famous one became "Big Willie". It went into production under the index "Mark I". The tank was mass produced in two variants: with two cannons and a machinegun or just machineguns. Modifications with one cannon and many machineguns also existed.
One of the main opponents of tanks in British military circles was Field Marshall Kitchener. Demonstrations of the "Big Willie" in February of 1916 in Hatfield Park (close to London) went far to turn his opinion on what he called "useless toys". The first trials, on February 2nd, were attended by the Minister of Armament and future Prime Minister D. Lloyd-George. The vehicle impressed him, but the stubborn Kitchener was not fully convinced until the second trials, attended by King George V. The stunned monarch immediately approved the production of tanks, and the military issued an order for 100 units.
Original article available here.