Can you swim in full plate armor? Video test!
So, this guy is a lot more optimistic about how the test went. His conclusion is a reasonably fit man who was used to wearing armor could swim, albeit for brief distances. I see a guy wearing 50 lbs of armor who can't keep his head above water for more than five seconds, if that. Maybe Michael Phelps could do better, but I'd bet a month's pay that even he couldn't swim half the length of an Olympic pool in that getup.