Same reason you need a lot of conventional warheads: targeting lists are long, and wartime commanders chew through ammo at a profligate and obscene rate.
- Nukes are a lot less destructive than people expect
- some targets are quite hard and require several weapons per aimpoint. Examples: Cheyenne Mountain, missile fields, railway marshalling yards
- many targets (especially tactical ones; see below) are dispersed. Often you need more than one weapon to target even a single ship.
- NATO and Soviet forces were built for an NBC environment
- this drastically lowers weapon effectiveness
- eg: hardening, dispersion.
- ICBM fields are spread out over hundreds of miles. Each silo/missile is many miles away from the next. No single warhead can destroy more than a single silo. Silos are hardened against conventional weapons and everything but a nuclear direct hit.
- USN ships operate in loose formation, many miles apart, for the same reason.
- Not all nukes are for blowing up cities.
- many are smaller, tactical weapons with many uses:
- torpedoes, mines, special demolition charges, artillery, land attack cruise missiles, anti-ship missiles, SAMs, ballistic missile defense, air dropped bombs, air to air missiles.
- most purposes were "conventional," you'll notice. You could use conventional explosives; it would just be slower
- so you need a lot more weapons than the opponent has cities.
- Many of those nukes are quite small
- Efficiency: 10x 100 kT nukes are more "efficient" than 1x 1,000 kT nuke.
- Bigger isn't always better:
- sub-launched nuclear torpedoes MUST be small, on the order of 10 kT. Since weapon range is short (~20 nmi), and water is incompressible and transmits shocks well, any larger weapon would destroy its own submarine. See also: SUBROC.
- warheads must be small enough to fit inside a missile, torpedo, backpack, artillery shell, etc.
- close support - large weapons risk hitting your own forces. Smaller weapons are more versatile.
- Many weapons will be destroyed (eg, first strike)
- a surprise first strike will destroy many of these weapons (ideally all)
- SSBNs are vulnerable
- the USN quietly tailed Soviet boomers for years. Eventually, the Soviet navy sequestered their boomers in bastions or deployed them under the arctic ice.
- Bombers are vulnerable.
- B-52 became completely outclassed by newer SAM systems.
- B-1B's original low-level mission became obsolete soon after it debuted.
- Both the B-52 and B-1B were relegated to standoff roles.
- Soviet naval aviation expected their bombers to be shot down in droves when attacking carrier groups.
- ICBM fields are very well known
- In a first strike, many ICBMs/MIRVs would be targeted at opposing ICBM silos.
- (In turn, these very hard ICBM silos served as warhead sinks)
- This prompted the Soviets to develop mobile ICBMs, which would be much harder to find.
- Airfields for bombers are very well known
- Inevitably, even some tactical weapons would be destroyed (airfield destroyed, aircraft shot down, sub accidentally lost)
- Your opponent will nuke your nukes. So the more nukes they have, the more nukes you need.
- Weapons will be defeated
- Land-based defenses: nuclear-armed ABM. See: Sprint, Nike-X, Sentinel, Safeguard, SDI ("Star Wars")
- Fleet defense: SAMs (against a/c and missiles), AAMs (against bombers and missiles), depth charges and torpedoes (against subs)
- See above and below
- Weapons will miss...
- A) because targets do not cooperate
- maneuvering
- EW
- decoys
- concealment
- B) because you don't know where the target is / you killed the wrong target
- you killed a rock
- you killed a fish
- you killed a seismic anomaly
- you killed a merchie
- you killed a friendly
- C) because the target is already dead (2nd and 3rd shot was just insurance)
- D) because the target is already dead (but you don't know this)
- E) because weapons miss
- Examples:
- the brits fired 50 torpedoes in the Falklands against just two obsolete Argentine subs (one from 1944); none hit. [context needed]
- historically, 50 SAMs have been fired for every aircraft shot down. [context needed]
- Ballistic missile defense
- See: Star Wars; ABM treaty
- note: perceived effectiveness
- eg, nuclear anti-missile missile. See: Sprint, a terminal ABM whose motors pushed 100 g's
- Nuclear weapon sharing
- Maintenance
- Miscellaneous
- margin for launch vehicle failure
- margin for warhead failure
- obsolete weapon not yet removed from service
- edit: Deterrence
I'm probably forgetting a couple (edit: deterrence!), but my point is that all those weapons serve a purpose. By and large, tactical warheads performed the same functions as conventional weapons. They just packed a bigger punch. Later, precision guided weapons would emulate
some of the effects of nukes, making the latter less necessary.
Basically, it's
not "clear that both sides had enough to annihilate the other."
