During the 1950s the USA thought that the USSR had many more long range bombers than it actually had. The Americans thought that the Russians had hundreds [actually tens] of bombers capable of dropping nuclear bombs on US mainland targets.
At the time air defences were rudimentary and the US military had a vision of their fighters being overwhelmed by fleets of Russian bombers. Air to air missiles were primitive so some means was needed of giving the US fighters a more powerful punch.
The answer was the Douglas AIR-2 Genie, an unguided air-to-air rocket with a 1.5 kiloton W25 nuclear warhead. The missile was carried by the F-89 Scorpion, F-101B Voodoo, F-106 Delta Dart, and F-104 Starfighter.
It didn’t have a proximity fuse or any guidance system. Pilots were expected to position their aircraft about 6 miles from where the enemy bomber(s) would soon be and fire. When an internal fuse burnt through the warhead exploded. The lethal range [fireball and blast] has been variously described as 300 metres and 1000 meters. The warhead also emitted a lethal blast of radiation but this could take five or so minutes to kill so a determined crew could still complete their attack on a nearby target.
The W25 warhead was also fitted to Nike missiles and batteries of these were set up around major cities. The blue dots on the map below shows the location of Nike batteries around New York.
If the Russians had ever attacked New York the inhabitants of the city would first have seen a series of bright flashes high in the sky from Nike and Genie warheads. Initially at some distance from the city, but getting closer. If they did not see enough flashes they would then have seen –
The Genie was only tested once, in 1957 above Yucca Flats during Operation Plumbbob. There is a video of the test. Five officers have voluntered to stand below the expected detonation point to demonstrate that the weapon could be used without danger to people on the ground. The height of the blast was between 18,500 and 20,000 ft above mean sea level.
Over 3,000 Genies were manufactured. The missile was retired in 1985.
Resurrection Day by Brendan DuBois  is an alternative history in which SAC launched an unauthorised attack on the Warsaw Pact during the Cuban Missile Crisis of 1962. Russia and most European countries are devastated and in 1972 SAC leaders are considered war criminals in most countries. America loses Washington, Omaha, and San Diego. New York is hit by three bombs when American fighters fail to stop all of a flight of Russian bombers. These losses and the resulting economic dislocation has reduced the USA to the status of a second world power.