Kocaeli Province (Turkish: Kocaeli ili , pronounced [kodʒaˈeli]) is a province of Turkey. Its capital is İzmit, which is sometimes referred to as Kocaeli itself. The largest town in the province is now Gebze. The traffic code is 41. The province is located at the easternmost end of the Marmara Sea, especially on the Gulf of İzmit. Because of the size and natural conditions of the Bay of İzmit, the city is a giant natural harbour. There are lots of harbour facilities within Kocaeli, including the primary base of the Turkish Navy.