I don’t think the example of Americans killed while fighting for Japan or Germany in World War II is an apt one in the discussions of whether we should worry about targeted drone attacks against American citizens, approved by unnamed administration officials. I think such a system is a bad idea for any administration.
The former cases were in declared wars against uniformed and almost always anonymous combatants, whose identities, not that it would have mattered much, as American citizens were usually known only later when they were killed or captured.
In contrast, we are talking about foreknowledge of killing known individual citizens, and not necessarily on a battlefield however loosely described. The better comparison would be Cold War–era assassinations against believed individual traitors or suspected rogue American operators in service to the Soviet Union or its Communist allies — who were gunned down in solitary fashion with precise knowledge of who they were. I am sure we did such things even if on rare occasions, and if we want to repeat that modus operandi, we should at least be honest enough to cite those examples as successful and necessary case histories that can now guide us in the present.