The calculated distance (air line) between Bonn and Mourmelon-le-Grand is approximately 164 miles respectively 264 kilometers.
By car or train, the actual journey to Mourmelon-le-Grand is certainly longer, as only the direct route (as the crow flies) between Bonn and Mourmelon-le-Grand has been calculated here.
Air line (approximately)
264 kilometers
143 nautical miles