Lonewolf,
The sites at which these weapons are held has been common public knowledge in Europe (to locals living near the air bases) ever since they were deployed. In the days before Hardened Aircraft Shelters (HASs) were built - before mid-1970s - all those NATO countries allocated US controlled tactical nukes mounted QRA (N) from open ended dutch barns - illuminated at night - with the weapons clearly visible on those aircraft types that carried them externally.
From 1995 they have all been held within Weapon Storage & Security System (WS3) vaults which retract into the floor of individual HASs. Full scale trials were done by the USAF bombing a HAS which destroyed the aircraft inside yet, when raised, the WS3 and dummy weapons were not in any way harmed.
It is in the public domain - in an article published in 2015 by the Federation of American Scientists - that significant upgrades are being carried out to security at Incirlik and Aviano.
Five NATO countries - Belgium, Germany, Italy, Netherlands and Turkey - still participate in the NATO Nuclear Sharing Program.
WS3:
