Kocaeli is a province of Turkey. Its capital is Izmit city, which is sometimes referred to as Kocaeli itself. The traffic code is 41. The province is located at the easternmost end of the Marmara Sea, especially on the Bay of Izmit. Because of the size and natural conditions of the Bay of Izmit, the city is a giant natural harbour. There are lots of harbour facilities within Kocaeli, including the primary naval base of Turkish Sea Forces.