Conversation so far:
Did Aleksandr Solzhenitsyn play a role in WW2?
During WW2, Aleksandr Solzhenitsyn served as the commander of a sound-ranging battery in the Red Army, was involved in major action at the front, and was twice decorated.
How long was Aleksandr Solzhenitsyn in the Red Army for?
In February 1945, Aleksandr Solzhenitsyn was arrested by SMERSH for writing derogatory comments in private letters to a friend about the conduct of the war by Joseph Stalin.
How many troops did Aleksandr Solzhenitsyn command as the commander of a sound-ranging battery in the Red Army?
Did WW2 have any effect on Aleksandr Solzhenitsyn?
While serving as an artillery officer in East Prussia, Aleksandr Solzhenitsyn witnessed war crimes against local German civilians by Soviet military personnel.
How did Aleksandr Solzhenitsyn react to seeing war crimes?
Of the atrocities, Aleksandr Solzhenitsyn wrote: You know very well that we've come to Germany to take our revenge for Nazi atrocities committed in the Soviet Union.

Question: Was he sorry he participated in WW2?
Self-contained rewrite: Was Aleksandr Solzhenitsyn sorry he participated in WW2?