ΔE 11.1, fair: the same colour family, but not a straight swap. Thunderhawk Blue is a little darker, more saturated, cooler than WWI French Artillery Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Thunderhawk Blue is a little darker, more saturated, cooler than WWI French Artillery Grey.
The same difference applies the other way round: WWI French Artillery Grey is a little lighter, more muted, 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 WWI French Artillery Grey on the colour wheel See Thunderhawk Blue on the colour wheel
All matches: WWI French Artillery Grey equivalents · Thunderhawk Blue equivalents