Douglas DC-4 R5D-1

Aircraft transferred to the United States Navy were designated Douglas R5D. The R5D-1 is 56 C-54As handed over, and from it came the R5D-1C — modified in service with a fuel system based on the C-54B's — and the R5D-1F staff transport, redesignated first R5D-1Z and then VC-54N.

The naval family continued with the R5D-2 (30 C-54Bs), the R5D-3 (95 C-54Ds), the R5D-4 (20 C-54Es), the R5D-5 — R5D-2s and R5D-3s re-engined to approximate C-54G standards — and the proposed R5D-6, a naval version of the C-54J that was never built. With the introduction of the Tri-Service designation system in 1962 all R5Ds became C-54s with new suffixes: the R5D-2 became the C-54P, the R5D-3 the C-54Q, the R5D-5 the C-54S and so on.