ΔE 19.1, loose: different enough that you should pick on purpose. Forest Green is noticeably darker, cooler than Militarum Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Forest Green is noticeably darker, cooler than Militarum Green.
The same difference applies the other way round: Militarum Green is noticeably lighter, 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 Militarum Green on the colour wheel See Forest Green on the colour wheel
All matches: Militarum Green equivalents · Forest Green equivalents