The Blue Homeland 2019 drill is Turkey's largest navy drill in its history, involving 103 vessels in all three seas surrounding the country, military sources say.
The German sub is part of what's known as Hitler's lost fleet‚ one of six U-boats sent to attack the Russian Black Sea Fleet in 1942.
Turkish Chief of General Staff Hulusi Akar says Ankara will never allow its interests in the Aegean and Eastern Mediterranean to be compromised.
Several members of the alliance feel concerned over Ankara's plan to purchase Moscow's sophisticated S-400 anti-missile defence systems.
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