I found this an utterly unbelievable story.
Story summary.USSR has been completely decimated in nuclear attacks by US.
But there still is a space based USSR fighting unit called Fort Lenin, on a "secret orbit beyond the moon", capable of completely wrecking the US.
Story is in the form of a recorded message from the President of Supreme Soviet, now dead, to this unit. Message tells them that they were meant as a deterrent, & obviously the deterrent hasn't worked. Now rather than a counter attack, they should quietly destroy their weapons & put themselves "at the disposal of the United States"!
Fact sheet."The Last Command", short story, review
First published: "Bizarre! Mystery Magazine", November 1965.