Probably old British army mine clearer's backpacks, modified in Denmark for more general military use by no other than the Danish King himself! Phew! One-off lot.
As simple as can be: a rectangular pack made of indestructible canvas with a lid secured with two straps. Carrying straps included! Unlike standard P37 straps, these have rather beautiful looking brass hooks on the ends.
Just slightly used at the worst. All in great shape.