Then by that defination, (if we agree with it) there were 52 "UNsuccessful" (even though they were operationally sound boats) American submarines during World War II which never returned to base. Would that be correct?
I will note a mear technicality that the C.S.S. Hunley, unlike some of these I mention, DID return to port. Although 140 years late and not in the condition that it originally left in, but with it's crew still aboard and at their Battle Stations.