The Piaget Tank watch in 18-karat yellow gold is an iconic model from the 1960s and 1970s, illustrating the brand's golden age in the field of ultra-thin watches and fine jewelry. The success of this model is based on the 9P caliber, launched in 1957. At just 2 mm thick, this manual movement enabled Piaget to create exceptionally slim cases (approximately 4.5 mm in total), a technical feat for the time. The 18-karat yellow gold versions are distinguished by a dial that is often white or champagne with black Roman numerals, a stepped case, and a crown adorned with a blue sapphire cabochon. Today, these pieces are sought after for their timeless elegance and historical significance in ultra-thin watchmaking. They represent a sophisticated and technically superior alternative (thanks to the 9P movement) to the more common rectangular models.