Was the US dollar, the Soviet reserve currency too?

Given the Soviet Union & the United States were engaged in a prolonged cold war where each tried to showcase the supremacy their political and economic systems, the two countries were in competition with each other.

The both sought the demise of the other while trying to gain as much influence internationally. The US would not have backed the Soviet ruble, instead it would have done what it could have to damage the ruble and ruin the Soviet economy to neutralize the threat that the Soviet Union then posed to the United States.

With the abandonment of the gold standard and the adoption of the 1944 Bretton Woods agreement, the US dollar eventually became the dominant currency used in international trade. It is for this reason that the Soviet Union had US dollars, so it could trade with non Warsaw Pact countries.

The Ruble wasn't backed by anything except the Soviet State. There were 2 completely separate economies in place within the USSR, one based on Rubles, one based on whatever foreign currency was available to the central bank. Technically there was a 3rd, a "certificate Ruble" that could be exchanged for foreign currency, but that was only available to foreign visitors and as a special reward for some citizens, and could only be used in certain special stores not open to the general public, with the exchange rate being set at whatever the Soviet central bank wanted.

So for foreign trade, you'd have to go to the appropriate government agency and request them to attain what you needed. They'd then go on the international market and purchase that for some of the very limited supplies of foreign currency available to the Soviet government. Ditto, if you had something to sell on the international market, you'd have to go through a government agency and they'd sell it for you, gaining foreign currency, and you'd then get paid by them in Rubles according to some imagined exchange rate (probably based on the amount you'd have gotten had you sold it within the USSR). Remember that it was actually illegal for most Soviet citizens to be in posession of foreign currency unless they were actually traveling abroad (which was pretty rare, most of them never left the country and would never get permission to do so if they requested it).

Clearing dollars

To understand why US dollar was reserve currency, you need to understand three things. One, US was definitely by far largest economy at the end of WW2. If you possessed US dollars, you could always trade them for US built goods which were plentiful. Consequently, traders across the world would also accept USD, effectively backing it up by not just US, but also world economy. Second, all of these above was formalized with Bretton Woods system, tying up other major (Western) currencies to USD. Finally, there was a petrodollar agreement where Saudi Arabia (and other Gulf monarchies) agreed to sell oil denominated exclusively in USD, in exchange for protection and backing of US and Western powers.

This left USSR in a predicament. Soviet ruble was backed by Soviet economy, but Soviet economy was much weaker then US economy. There were some things you simply could not buy with rubles, even if you had enormous quantities of them, because Soviet Union did not produce them. To back ruble with gold or silver was out of the question (even US abandoned gold standard) because there was simply not enough of these precious metals. There was a official exchange ratio between USD and ruble, but nobody in his right mind would sell dollars at that price unless forced to do so. Unofficially, ruble was worth much less on the black market, and people were still buying USD at inflated prices in order to purchase some consumer goods smuggled from the West or simply to use them as savings. Even countries in Soviet Block where not too keen to trade in rubles, and preferred USD when they could get them, because with USD they could trade not only with the West, but also with countries keeping themselves neutral in Cold War.

So what was to be done then ? Answer was clearing dollars. This simplified works like this: Neither you or I have USD because we do not trade much with evil capitalists in the West :) But, I have some fighter aircraft and you have grain. We agree that my fighter aircraft are worth $80 million, your grain $100 million, and IOU $20 million. Sometimes latter I could send you $30 million worth of cabbage, and you will send me $10 million worth of timber, and we are settled.

In this manner, although neither of us had real USD, we could still use them as a tool for barter. Of course, prices on these agreements would vary, sometimes they were realistic market prices at the moment, sometimes USSR helped some countries in order to gain prestige, sometimes those countries sold at discount etc ...