The Pentagon has released its Nuclear Posture Review,dated February 2018.Secretary of Defense Jim Mattis contributed a preface to the document.Here are some excerpts of his thoughts on the subject:
This review comes at a critical moment in our nation's history,for America confronts an international security situation that is more complex and demanding than any since the end of the Cold War.In this environment,it is not possible to delay modernization of our nuclear forces if we are to preserve a credible nuclear deterrent-ensuring that our diplomats continue to speak from a position of strength on matters of war and peace.*
While Russia initially followed America's lead and made similarly sharp reductions in its strategic nuclear forces,it retained large numbers of non-strategic nuclear weapons as well as its other strategic systems.Even more troubling has been Russia's adoption of military strategies and capabilities that rely on nuclear escalation for their success.These developments,coupled with Russia's seizure of Crimea and nuclear threats against our allies,mark Moscow's decided return to Great Power Competition.*
This review confirms the finding of previous NPRs that the nuclear triad (sea,air and land-based systems) - supported by NATO dual-capable aircraft and a robust nuclear command and control system - is the most cost effective and strategically sound means of ensuring nuclear deterrence.To remain effective,however,we must recapitalize our Cold War legacy nuclear forces.*
Modernizing our dual-capable fighter bombers will maintain the strength of NATO's deterrence posture and maintain our ability to forward deploy nuclear weapons,should the security situation demand it.*
I would be remiss if I did not acknowledge the vital role our Soldiers,Sailors,Airmen,Marines and Coast Guardsmen,and civilians play in making a safe,secure and ready nuclear force.Without their ceaseless and often unheralded efforts,America would not possess a nuclear deterrent.At the end of the day,deterrence comes down to the men and women in uniform - in silos,in the air,and beneath the sea.
To each and every one of them,I wish to express my personal respect and that of a grateful and safe nation.
                                                                     
                                                                         Signed,
                                                                        Jim Mattis*
According to NATO:
Nuclear weapons are a core component of NATO's overall capabilities for deterrence and defence,alongside conventional and missile defence forces.The circumstances in which any use of nuclear weapons might have to be contemplated are extremely remote.
Strategic nuclear forces:
As stated in the 2010 Strategic Concept:
The supreme guarantee of the security of the Allies is provided by the strategic nuclear forces of the Alliance,particularly those of the US;the independent strategic nuclear forces of the UK and France,which have a deterrent role of their own,contribute to the overall deterrence and security of the Allies.
Dual-capable aircraft:
A number of NATO member countries contribute a dual-capable aircraft (DCA) capability to the Alliance.These aircraft are available for nuclear roles at various levels of readiness - the highest level of readiness is measured in weeks.In their nuclear role,the aircraft are equipped to carry nuclear bombs and personnel are trained accordingly.The US maintains absolute control and custody of the associated nuclear weapons.
Allies provide military support for the DCA mission with conventional forces and capabilities.*
According to the Nuclear Threat Initiative think tank:
About 150 US gravity bomb B-61 warheads are currently stored in Europe.
There are six nuclear weapon facilities in five NATO countries:Belgium;Germany;Italy;the Netherlands;and Turkey.
Dual-capable aircraft currently include:US F-15 E;F-16 C/Ds;Belgian,Dutch and Turkish F-16s;German and Italian PA-200 Tornados*
The US Coast Guard helps provide security for US ballistic missile submarine bases,plus emergency support for the subs such as medevac as needed.