Some more tidbits:

The VW Typ 82 Kbelwagen (cheaper jeep equivalent of WW2) was required to have a gear for foot march speed. It was meant to allow 4 km/h minimum speed.


Another detail:
I read a book about pre-WWI militaries in Europe (great power, focus on Germany and Austria-Hungary) again.
It mentioned
30 km required foot march / day
25 km practical march / day
50 km as one-time only exceptional forced march