In 2019, a NATO-affiliated body released and subsequently deleted a document that apparently confirmed something that had been suspected for a long time - U.S. nuclear weapons are being stored at air bases in several European countries. A copy of the document was published by Belgian newspaper De Morgen which stated that B61 nuclear bombs are stored at six bases in Europe.
As a factsheet from the Center for Arms Control and Non-Proliferation details, the bases in question are Kleine Brogel in Belgium, Büchel in Germany, Aviano and Ghedi in Italy, Volkel in the Netherlands and Incirlik in Turkey. The presence of the weapons stems from an agreement during the Cold War in the 1960s aimed to deter the Soviet Union and convince the countries involved that starting their own nuclear weapons programs was not necessary.
The B61 is a low to intermediate-yield strategic and tactical thermonuclear gravity bomb which features a two-stage radiation implosion design. It is capable of being deployed on a range of aircraft such as the F-15E, F-16 and Tornado. It can be released at speeds up to Mach 2 and dropped as low as 50 feet where it features a 31 second delay to allow the delivery aircraft to escape the blast radius.