I read somewhere recently that by the time the USSR collapsed, it only had 1/8th the GDP as the United States. This struck me as somewhat humorous and revealing, as it really dispels the notion that the Cold War was between "two equal powers," at least towards the end of it.
So in that regard, when WAS the economy of the USSR as close to the US's? Was this considered a legitimate problem by the US government, or was it mainly their military and nuclear capabilities that scared them?
Well, let's take a look at some graphs!
Here we have the USSR's economic history from 1970-1990. They peaked at ~1 trillion dollars ~1980.
This is lower than any point of the US during that same period. Same source.
At no point in time was the economy of the USSR close to that of the US during the Cold War. They peaked below the GDP of the US in 1970.
At no point in time was the USSR's economy equal in any way to that of the US.
But in many ways, the threat to the US, from an economic point of view, was the pace of growth and the "sturdyness" of the Soviet economy. The two sweetspots when these advantages were more evident were during the Great Depression and during the first two decades of the Cold War. From 1970 onwards the USSR started to falter and falter with regards to the US economy, until its final demise in 1991.
That being said, it would have been nothing short of a miracle for the Soviet economy to match the US one, considering how the latter has a higher population and started its industrialization centuries before Russia did.
During the Great Depression what was surprising was how all of the staunchly capitalist Great Powers (US, UK, France) were basically on their knees, with incredibly high unemployment, virtually no growth and the social maladies that appear whenever these two are present.
Meanwhile, the USSR was posting gains and beginning its brutally harsh industrialization. The Soviet economy, completely isolated from world markets, was able no navigate the 1930's untouched by the troubles that the capitalist countries were experiencing. It is worth noting, that underscoring the improbability of the Soviet industrialization is the fact that a mere 10 years before, Russia was in the midst of a bloody and brutal civil war in which (to Russia's humiliation) all of the (now ailing) powers had participated (US, UK, France, etc) against the Bolsheviks.
The second sweet spot was during 1945-1970 during which Russia continued its heavy industrialization, and helped its Eastern European clients do the same. In fact, in Europe the communist economies as a whole grew faster than capitalist ones. Such growth was what attracted a lot of leaders of third world countries to the communist camp. Many of these leaders were heads of recently independent countries, and they were eager to industrialize and modernise their economies.
Ultimately, the Soviet economy's strength was also its weakness. In many ways, the USSR froze after the death of Stalin and remained in that form until its collapse. Its economy was centrally planned and decision making power was concentrated in a single authority. And while this made it very forward-driven, it also meant that it was very inflexible and unable to adapt to changing circumstances.
While during the first two decades of the Cold War, the USSR mainly exported capital goods and manufactured products. By the time the 1970 came it was mainly exporting fuel (gas, oil) due to the rising oil prices (courtesy of OPEC), its manufacturing sector being unable to compete even against the industries inside its own block. It started exporting what usually third world countries export: raw materials.
All in all, the threat to the US came, after the 1970, solely from the Soviet military. The Stalinist centrally-planned economy was woefully inadequate to compete with a capitalist one.
Source: Hobsbawm, The Age of Extremes.
As a curiosity point, was the economy of Russia ever matched with that of the early U.S? If so, when did we overtake them?