Here come the boring statistics, it will be a long answer.
The invasion of Cuba was OPLAN 316 [Operational Plan].
Cuba had 17 divisions with a total of 130,000 all ranks: 1 armoured, 3 motorized, and 13 infantry. Tanks were mainly Soviet T-34s.
The Soviets had a Motorized Rifle Division on Cuba of 4 Motorized Rifle Regiments instead of the normal 3. Further, they had 2 SAM divisions with 144 S-75 Dvina [SA-2 “Guideline”] launchers, a Fighter Aviation Regiment of 40 MiG-21s [“Fishbed”], a Transport Helicopter Regiment of 33 Mi-4s [“Hound”], and a Fighter-Bomber Squadron of 17 Il-28 [“Beagle”].
Nuclear forces in Cuba consisted of 2 Frontal Cruise Missile Regiments with a total of 80 FKR-1 coastal defence missile on 16 launchers. These had a 20 kt warhead. There were 3 MRBM Regiments with a total of 36 R-12 (8K63) Dvina [SS-4 Mod.1 “Sandal”] missile and 24 launchers. Each R-12 had an 8F126 warhead at 2.3 Mt. There were also 2 IRBM Regiments with a total of 24 R-14 (8K65) Usovaya [SS-5 Mod.1 “Skean”] missiles and 16 launchers. Each R-14 had an 8F15 warhead also at 2.3 Mt. There were 3 Rocket Regiments with a total of 12 3R10 Luna-2 [FROG-5] rockets and 6 launchers. Each Luna-2 had a 3N14 warhead at 20 kt. Finally, there were 11 RDS-4M Tatyana free-fall bombs at 28 kt each to be delivered by the 6 Il-28N bombers [the other eleven Il-28s were non-nuclear-capable].
The Americans were not aware of the tactical nuclear weapons, this is important to realize.
The US invasion plan would have unfolded as follows. On D-Day, the USAF would have flown 1,180 sorties with the F-4 Phantom, the F-100 Super Sabre, the F-105 Thunderchief, and the F-104 Starfighter series of aircraft. Their main targets were the MRBM and IRBM launch sites, the airfields, and the SAM nests. These aircraft were stationed on airbases in Florida, Alabama, and Louisiana. On D+1 a total of 786 sorties were planned and somewhere between 700–800 for the following days.
The USMC would operate the AF-1E Fury in the air defence role over Guantanamo Bay. At this point, no carrier operations were planned although carrier-borne aircraft were on standby should the USAF losses prove to be too high. Since nobody had flown in an environment with so many SAMs, the USAF had no clue what its losses would be.
On D+2 the amphibious landings would have taken place around Havana. A brigade-sized Task Force from the 1st Armoured Division would support the 2nd Infantry Division. Also on D+2, the XVIII Airborne Corps consisting of the 82nd and 101st Airborne Divisions would be parachuted in Cuba. D+3 would see the deployment of the 4th Infantry Division while on D+7 the rest of the 1st Armoured Division would follow.
The USMC would land an Expeditionary Brigade on D+5 in Guantanamo Bay and would push land inwards from the East.
Soviet General Pliyev had nuclear release authority for the tactical nuclear weapons but not for the strategic MRBMs and IRBMs. This means he would have hit the American invasion fleet with FKR-1 coastal defence missiles and Luna-2 rockets. This nuclear barrage would effectively destroy most of the US troops landing.
NATO had a First Strike Policy in place, the nuclear war plans had zero flexibility.
The moment the US invasion fleet is destroyed, Strategic Air Command would have executed SIOP-63 [Single Integrated Operational Plan]. 2,952 strategic nuclear weapons would have been used against the Communist Block within 8 hours.
The US had 224 ICBMs on alert: 142 C/HGM-16D/E/F Atlas D/E/F, 62 HGM-25A Titan I, and 20 LGM-30A Minuteman IA. The first wave consisted of 49 ICBM launches followed within two hours by the rest. This would effectively take out a substantial chunk of the Soviet Air Defences and allow the bombers to penetrate.
The bomber force consisted of 540 B-52D/E/F/G/Hs Stratofortresses, 790 B-47B/Es Stratojets, and 72 B-58As Hustlers. They were equipped with the AGM-28A Hound Dog [on some B-52s] and with mainly Mk-15 and B28 series free-fall bombs. The Hound Dogs had a yield of 1.1 or 1.45 Mt, depending on the type of warhead. The free-fall bombs had yields between 350 kt and 1.69 Mt. Some B-58A Hustlers would carry the Mk-39 series with a yield of 3 or 4 Mt against command bunkers. They would dash in and take out the bunkers around Moscow.
The US Navy would fly 62 aircraft against the Soviet Union. All A-4B/C/E Skyhawks carrying B28 series free-fall bombs. The Navy had two Washington-Class SSBNs on patrol with 16 UGM-27A Polaris SLBMs with a 600 kt warhead; and two Grayback-class each carrying 4 RGM-15A Regulus II cruise missiles each carrying a W-27 Mod.1 warhead at 2 Mt all aimed at the Soviet Union.
Cuba would have been hit by 14 tactical nuclear weapons, all B28s, while North Korea would have been hit by 35, and China by 60. The Nuclear Operations Plan of NATO had allocated a further 3,011 nuclear weapons against Eastern Europe varying from battlefield rockets, over cruise missiles and free-fall bombs, to strategic weapons carried by the British V-Bomber Force. These attacks would have been executed within the first 5 hours of the war.
Follow up nuclear attacks were planned with an undefined number of nuclear weapons, depending on how well the war was going. The British had 175 nuclear weapons, the US 27,387.
The first wave would kill an estimated 37% of the Soviet population. The ultimate aim was to destroy 75% of the Soviet military, 90% of the industry, 75% of all housing, and to kill 55% of the entire Soviet population within 72 hours.
The Soviets had 3,322 nuclear weapons of which only 149 were on alert. Most of these weapons would have been destroyed in the NATO Nuclear First Strike.
It is doubtful the Soviets would have been able to hit even a couple of targets within NATO and other Western countries.