Patek Philippe introduced the Aquanaut model to the market in 1997, inspired by the success of the design of the Nautilus model. The shape of the Aquanaut case features the same port-hole design, but was also water resistant to 120m. The watch also featured an unusual composite "tropical" strap, to resist saltwater immersion and deterioration, as opposed to the more traditional metal bracelet or leather strap. The present example is featured on the stainless-steel bracelet from Patek, which is less common. This model unlike the Nautilus can feature a bracelet or "tropical" strap. In 2007, the reference 5167 series was launched, featuring a more subtle textured dial and a larger case, measuring 40mm diagonally across the case. The 5167 is one of the most sought after modern Patek Philippe watches on the market.