They were not challenged. The U.S. nuclear weapons based in Europe are in the sole possession and under constant and complete custody and control of the United States. NATO's nuclear weapons are stored under highly secure conditions. They have been well-tested and meet the highest safety standards. The U.S. PAL devices ensure an additional safeguard against accidental or unauthorized use.
Allies are confident in the safety and security of their nuclear weapons.
These national political commitments contribute to global non-proliferation efforts. In NATO, the final decision on any employment of nuclear weapons would be taken by the Alliance's nuclear-weapon States. Thus, NATO strategy is in full compliance with the NSAs. In 1996, the ICJ issued an advisory opinion on the legality of nuclear weapons. Allies are convinced that the role of nuclear weapons in NATO's strategy fully conforms with international law.