The Unit 631 was a special team of exobiologists and organic chemistry specialists . Their purpose was to study the Element 631 microorganism that was gathered after the " North Strelka Meteor " incident.
When the Nuclear War began , all the data and samples were lost and the members of this unit went MIA/KIA.
Even nowadays there is no information to know if they survived or not .
Their facilities were presumed wiped out by several atomic warheads in the early hours of the war.