ΔE 11.8, fair: the same colour family, but not a straight swap. Steel Legion Drab is noticeably lighter, cooler than NATO Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Steel Legion Drab is noticeably lighter, cooler than NATO Brown.
The same difference applies the other way round: NATO Brown 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 NATO Brown on the colour wheel See Steel Legion Drab on the colour wheel
All matches: NATO Brown equivalents · Steel Legion Drab equivalents