Was doing some reading and came across this graph. Now assuming this chart is accurate the USSR would seem to have believed that simply possessing more nukes would give them some sort of advantage. This runs contrary to my understanding of MAD so what was the thought process of Soviet leadership then and is my assumption that they were misguided a flawed belief.
Here's a quick graph I made that sheds a little more light on the situation: most of those Soviet warheads were tactical nukes, used for fighting on a battlefield, not aimed at the cities of a nation on another continent. (Apologies about calling them "Soviet" post-Cold War — as I said, it was a quick graph!) There are some interesting trends on the graph:
The US built a huge number of tactical weapons in the 1960s then got rid of most of them. This was in part as it shifted away from the idea of winning "limited" nuclear, and began to fear that tactical weapons could escalate things.
If you look only at the number of strategic weapons (weapons aimed at cities, bases, etc.), it's the US that seems to build huge arsenals "for their owns sake," well ahead of any Soviet arsenal. The US strategic arsenal was over 10,000 weapons from 1965 until 1991, while the Soviet strategic arsenal only cracked 10,000 in 1984.
These numbers can be a little misleading with regards to strategic weapons, because they don't take into account the number of launchers. Example: in 1986, the US had about 1,000 ICBMs, but they were armed with 2,165 warheads — because some of the ICBMs had multiple warheads on them. With submarines it is even further off — in 1986, the US had 616 SLBMs, armed with 5,440 warheads. The Soviets, by contrast, had 1,370 ICBMs, armed with 6,812 warheads, and 948 SLBMs, armed with 2,280 warheads. So from just these rough numbers you can see that there were some differences in approach — Soviet subs had less MIRVing at that point, but their ICBM force was heavily MIRVed. Which is all just to point at the fact that raw warhead counts don't tell you what the war would actually look like, or how the forces were deployed.
Why'd the Soviets build so many tactical weapons relative to the US? That I'm not sure about. My suspicion is that many of these were used in defensive ways, e.g. anti-bomber or anti-plane weapons (e.g., a "tiny" nuclear weapon attached to an air-to-air rocket). But I don't have a number breakdown in front of me. It could just be that they anticipated potentially having to use them in a land war (the Soviets were nothing if not afraid of invasion — their experience in WWII left a psychological mark). And there may be other, more internal reasons for such a thing (e.g., in the US the interservice rivalries were partially responsible for the "overkill" of weapons — each service wanted its own "cut" from the nuclear pie).
But anyway. If you look at the numbers, you don't see the Soviets mindlessly acquiring nukes for their own sake. You see 1) them still trying to "catch up" with the US in terms of strategic weapons (there were more weapons aimed AT them than they were aiming outward), and you see 2) a heavy production of tactical nuclear weapons, which stops dramatically in 1986 (it is worth noting how dramatically the US policy changed in this regard as well, in 1964).
Separately it is worth noting that Soviet missiles were notoriously less accurate than American ones. A consequence of lowered accuracy is a need for increased warhead sizes, but also potentially more warheads (if you want to guarantee destruction of a target). So the Soviets had strategic incentives to have large arsenals even if they didn't have +10,000 strategic weapons aimed at them for all of those decades.
On Soviet strategic and tactical policies, see Pavel Podvig's Russian Strategic Nuclear Forces. Data on the above comes from a combination of sources, including the Bulletin of the Atomic Scientist's Nuclear Notebook series, as well as several defunct web pages created by the National Defense Resource Council.
