Shortly before the war, Germany gained diplomatic favor over Great Britain in the Ottoman Empire.

The Ottoman Empire was a desirable ally at this point because of its strategic location on the Med and relative weakness compared to most European powers. Great Britain was the main ally of the Ottomans, but they let their diplomacy lapse and Germany used the opportunity to gain their favor.

In return for political support, the Turks got all sorts of neat military equipment including small arms and two German cruisers. The cruisers included a mostly or entirely German crew, as did some of the more "technical" positions such as artillery and, I believe, aviation personnel.

Sources: Alan Moorehead's "Gallipoli" and Michael Hickey's "Gallipoli" both detail the German diplomatic efforts with the Ottomans.

Not to forget that the Germans had been eyeing the Ottoman Empire for a very long time, wishing for it to become what India already was to the British.