Enola Gay had 1 bomb (16 kiloton), killing 100 000 in Hiroshima.  1 Trident sub can carry 100 Hydrogen bombs, equivalent to 1000 Hiroshima bombs.

The smallest Trident missile (multiple war heads, range from 0.3 to 100 kiloton) would kill 500 000 people.

Blast wave wind approaches speed of sound. Central area of total destruction (airburst helps because reflection of blast from ground creates constructive interference. Radiation outside takes a few weeks to kill other people.  6 mile outer circle suffers “Flash” (visible light, infrared and ultraviolet) causing 3rd degree burns and combustion of clothes etc.  Building cover and terrain v important here.  In smaller weapons, blast wind may put out many of these fires, but with bigger weapons, wind strength falls off more quickly than light energy. Hiroshima suffered a fire storm, Nagasaki did not (prob related to lower density of combustible material, terrain etc).

Russia and US each have 4000 weapons, enough to drop 10 on every city over 100 000 people.

Collateral effects are not considered by military.  Fire damage resulting from nuclear blasts could result in high level smoke (above rain clouds) around the entire globe within weeks, causing massive agricultural losses lasting years. Starvation would of course affect poorest. Estimated 1-2 billion deaths if nuclear war between India and Pakistan.

US has launch on warning capability.  President can launch within minutes using nuclear “football” (briefcase) carried by accompanying military officer, without consultation. Secretary of defence must verify identity of President but cannot veto order.