Führer wanted Turkey in axis from start,because of interests and relations with Turks.
In WW1 Germans and Turks fought together aganist their mutual enemies in same fronts.
For example ; Germans sent officers to Turkey,and Turks sent 20.000 Soldiers to Galician front to aid German Army.
Hitler stoped Italians to invade Turkey with their forces in aegean islands before WW2 (most of them was at rhodes,40.000 soldiers) , sent officers to help creation of Turkish self-product airforce and plane factories etc.
Turkey had good natural resources which German Army needed.Germany had non agression,friendship etc pacts with Turkey.
In both 1941 and 1943 Germans invate Turkish Officers to Fronts for convince them to join at axis’ side.
But it was nearly impossible for Turkey because Turkey was surrounded by three powers.
Soviets in east,allies in south,Germans in west.President couldnt take risk
“One of the purposes of this military demonstration(video below) was to show how powerful the German War Machine was, and convince Turkey to join the war on Germany’s side. This demonstration took place jut before the Operation Citadel (7 July 1943) under te name of “Türkenübung”. Turkish Generals and Officers observed soldiers and equipments with German officers and General Field Marshal Erich von Manstein.”
Here is the video :
Some photos :
Adolf Hitler,Turkish Gen.Cemil Cahit Toydemir,Feldmarschall Keitel and Turkish Officers at Wolfsschanze
Plus + photo of Turkish Hitlerjugend - 1934