Kocaeli Province (Turkis: Kocaeli ili , pronounced [kodʒaˈeli]) is a province o Turkey. Its caipital is İzmit, which is sometimes referred tae as Kocaeli itsel. The lairgest toun in the province is nou Gebze. The traffic code is 41. The province is locatit at the eastmaist end o the Marmara Sea, especially on the Gulf o İzmit. Acause o the size an natural conditions o the Bay o İzmit, the ceety is a giant natural harbour. There are lots o harbour facilities athin Kocaeli, includin the primary base o the Turkis Navy.