From Military Post Office to Army Battalion in 1918

This cover was sent from the ambulant post office in the Belgian Army (Postes Militaires - Legerposterij) to another such ambulant post office on 2 October 1918.

Characteristics: Nice block of 4 Clear cancels No cancel of arrival on reverse side but cover appears to have traveled Two fold lines, likely due to the addresse having folded the letter upon receipt to put it in his pocket. Some fading on the bottom half
Estimated value: $60