Perhaps a cap badge due to the two lugs on the reverse of the badge but other than that no idea. The crossed cannons and the flaming grenade make it almost certain to be artillery but what country? Its most certainly not a British crown sitting atop.
REGIS ULTIMA RATIO reads the latin scroll inscription
Belgium as one of the beligerants of the great war participated in the issue of UN named medals to its combatants after the 1918 armistace. On the Obverse a stylized eros has its arms extended. On the reverse a wheel of the coats of arms of the Belgian provinces surround the central Belgian lion.