ΔE 16.4, loose: different enough that you should pick on purpose. Prussian Blue is a little darker, much more saturated than IJN Gray (Sasebo Arsenal).
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Prussian Blue is a little darker, much more saturated than IJN Gray (Sasebo Arsenal).
The same difference applies the other way round: IJN Gray (Sasebo Arsenal) is a little lighter, 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 IJN Gray (Sasebo Arsenal) on the colour wheel See Prussian Blue on the colour wheel
All matches: IJN Gray (Sasebo Arsenal) equivalents · Prussian Blue equivalents