The NATO exercises, focused on submarine rescue operations and called "Dynamic Monarch", were taking place yesterday in Turkish waters in the Mediterranean Sea off the resort city of Marmaris and involved 1,000 personnel and nine countries including France, Britain and the United States.
The drill, the first in Turkey since 2000, is aimed at demonstrating multinational submarine rescue cooperation and interoperability. But its hosting by Turkey is also a symbol of Ankara's importance within the alliance during a tense period.
A NATO official, who asked not to be named, added: "Turkey is essential for the security of Europe. It has NATO's second largest army and makes an important contribution to the alliance including our missions in Afghanistan, Kosovo and the Aegean Sea."
The manoeuvres got underway earlier this month and the press were permitted to witness the drill yesterday, with the operation due to wrap up tomorrow.
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However its relations with several key alliance members, in particular Germany, have been damaged over the merciless crackdown after last year's failed coup.
Ankara in turn accuses EU states of failing to round up Kurdish militant and coup plot suspects.
Ties with the United States meanwhile have been hurt by Washington's support of a Syrian Kurdish militia Ankara regards as a terror group.
The exercises come just a week after Turkey ruffled feathers within NATO by announcing it had signed a deal with Russia to purchase Moscow's sophisticated S-400 air defence systems.
Analysts have however warned that despite the signing, thorny issues still need to be resolved before delivery including Turkey's demand for technology transfer and Russia's order backlog for the hardware.
Financial details have not been disclosed but according to Russian press reports the deal is worth USD 2 billion with Turkey seeking a credit from Russia to assist the payment.