As its m number suggests, this type of cap was introduced in 1915 and it was used up to the 1940 when Belgium was defeated by the Germans.
The example I recently picked up is for an officer and dated to the inter war period. My understanding is that he was a junior officer with the III (3rd) division -Arabic numerals are for regiments, Roman numerals for divisions- and was with the Engineers, being black and red. If it was a collar patch is would be black with red piping, but in this case the black tassel with red piping to the cap means the same, though I am still working on this subject.