A nuclear triad refers to a nuclear arsenal which consists of three components, traditionally strategic bombers, intercontinental ballistic missiles (ICBMs), and submarine-launched ballistic missiles (SLBMs). The purpose of having a three-branched nuclear capability is to significantly reduce the possibility that an enemy could destroy all of a nation’s nuclear forces in a first-strike attack; this, in turn, ensures a credible threat of a second strike, and thus increases a nation’s nuclear deterrence.
Russia and the United States possess nuclear forces consisting of land-based missiles, ballistic or long-range cruise missile submarines, and strategic bombers or long-range tactical aircraft.
China is expected to pass a military milestone this year when it sets a different type of sub to sea—a “boomer,” carrying fully armed nuclear missiles for the first time—says the U.S. Office of Naval Intelligence, or ONI.
China can launch cruise missiles from its HK6 strategic bomber and China has had land based nuclear missiles for a few decades.
Israel has been suspected of having a nuclear triad capability since about 2007.
Israel has been reported in congressional testimony by the US Department of Defense of having aircraft-delivered nuclear weapons as early as the mid-1960s, a demonstrated missile-based force since the mid-1960s, an IRBM in the mid-1980s, an ICBM in the early 2000s and the suspected second-strike capability arrived with the Dolphin-class submarine and Popeye Turbo submarine-launched cruise missile.
France was a former triad power. The French Force de frappe possesses sea-based and air-based nuclear forces through the Triomphant-class ballistic missile submarines deployed with M45 intercontinental SLBMs armed with multiple warheads, nuclear capable Dassault Rafale F3 and Dassault Mirage 2000N fighter aircraft which replaced the long-range Dassault Mirage IV supersonic nuclear bomber and KC-135 aerial refuelling tankers in its inventory. France had S2 and S3 silo based IRBMs, the S3 with a 3,500 km range, but these have been phased out of service since the dissolution of the USSR. France operates aircraft with a nuclear strike role from its aircraft carrier.
The UK possesses sea-based nuclear forces through its Royal Navy Vanguard-class ballistic missile submarines, deployed with Trident II intercontinental SLBMs armed with multiple warheads. The UK could have deployed land based missiles but did not bother because the size country is too small. The small size means it did not make strategic sense to have land based missiles when the threat was from the Soviet Union/Russia.