ΔE 15.5, loose: different enough that you should pick on purpose. Cobalt Green is a little darker, cooler than Army Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Cobalt Green is a little darker, cooler than Army Green.
The same difference applies the other way round: Army Green is a little 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 Army Green on the colour wheel See Cobalt Green on the colour wheel
All matches: Army Green equivalents · Cobalt Green equivalents