Presumably in the early 1950s, Commando K confronted Dr. Gearbox in Alaska. Though, the doctor was trying to escape and defect from Soviet Russia, his intentions were misinterpreted by U.S. authorities. Commando K destroyed Fafnir, a dragon like robot creation built by Dr. Gearbox during the skirmish.
It's not known for sure if Commando K was just one hero or a group of some kind of advanced soldiers. The headline is vague. And the mention in A Visitor's Guide about Slugger being a part of the project again could mean that the project was an elite unit of soldiers.
Also unknown is whether or not getting "lost" was Commando K's final fate or merely a temporary one.