Sponsons were built separately from tanks, not necessarily by the company that built the actual tanks.
This framework of wood and wire-netting (chicken wire the Americans call it) was devised as a means to prevent enemy stick grenades from lodging on the roof of the tank.
Historian Dan Snow presents this bite size history of the tank in the First World War, filmed on location at The Tank Museum.
One object, The Henriques Ring, now on display in the new Tank Men exhibition offers a fascinating and very personal link to the first tank attack in history.
In 1915 the First Lord of the Admiralty, Winston Churchill, created a Landships Committee to tackle the problems of trench warfare.
The Tank Museum is marking the centenary year of the first tank attack in history with a new exhibition titled `TANK MEN` focussing on pioneering tank soldiers.
While it is undoubtedly the oldest surviving tank in the world Little Willie was only ever a prototype, it was the only one of its kind ever built.