Biggest Tank of WWI - Sturmpanzerwagen A7V

Tanks were first developed during World War I as a method to cross the deadly 'no man's land' between opposing lines. Trench warfare was bloody, with ground being taken and given slowly. It began to take it's toll on both armies. Each side began developing armored vehicles to break the stalemate.

The British military was the first to introduce these new 'tanks'. The Germans needed a solution to counter the newly arrived British tanks. They quickly designed and built their own. The result was a monstrosity called the Sturmpanzerwagen A7V.

A behemoth of a tank, the Sturmpanzerwagen A7V had a crew of 18 men and weighed in at 73,700 lbs. With a top speed of 5-9mph (depending on the terrain) and a range of 25 miles, the A7V was a lumbering, unreliable beast of a tank, and was unable to compete with the Allied tank corps.

Source: Deutsches Bundesarchiv (German Federal Archive)

Sources:
http://www.historyofwar.org/articles/weapons_a7v.html
http://mailer.fsu.edu/~akirk/tanks/ww1/WW1.html