The DC-4 was also introduced in the 1930s: http://en.wikipedia.org/wiki/Douglas_DC-4

All private, I think. This one flies right over our office several times a week: http://archives.californiaaviation.org/ganews/msg09194.html .

Most are privately owned or with historical flights, but some do remain in military service. For instance, the Salvadoran Air Force operates 2 near-original C-47Ds and a few Basler BT-67s and the South African Air Force has 10 C-47TPs (converted to turboprop power with PT-6A engines) which are used in the maritime patrol, light transport and EW roles.