ΔE 11.8, fair: the same colour family, but not a straight swap. RLM 83 Dark Green is noticeably lighter, cooler than Dark Drab.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). RLM 83 Dark Green is noticeably lighter, cooler than Dark Drab.
The same difference applies the other way round: Dark Drab is noticeably darker, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Dark Drab on the colour wheel See RLM 83 Dark Green on the colour wheel
All matches: Dark Drab equivalents · RLM 83 Dark Green equivalents