Louis Cartier did more for watchmaking than one might imagine. At the turn of the twentieth century, he was among the first to propose wristwatches, a style that would overtake pocket watches in popularity from the 1930s. He also had a jeweller's eye for design which he applied to some of the earliest form watches, the majority of which are still part of Cartier's catalogue today. The Tank is one. It first appeared as a prototype in 1917 before becoming commercially available two years later. Legend has it that Louis Cartier found the idea for the original square shape, and the "brancards" on either side, in the hull and tracks of the Renault tanks that took part in the terrible Battle of the Somme in 1916. This wasn't, however, a design set in stone as the Tank evolved to please changing fashions and customer demand. By 1920 its case had adopted a more elongated form to become the Tank Cintrée. 2018 marks a milestone as its signature Roman numerals are replaced by Arabic numerals. The case is proposed in yellow gold, pink gold or platinum.