ΔE 35.8, loose: different enough that you should pick on purpose. Khaki Drill is noticeably lighter, much more saturated than Warm Brown.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 36). Khaki Drill is noticeably lighter, much more saturated than Warm Brown.
The same difference applies the other way round: Warm Brown is noticeably darker, much more muted.
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 Warm Brown on the colour wheel See Khaki Drill on the colour wheel
All matches: Warm Brown equivalents · Khaki Drill equivalents