Intended as a shore bombardment vessel, M18s primary armament was a single 9.2 inch Mk X gun which had been held as a spare for the and. In addition to her 9.2-inch gun, she also possessed one 12 pounder and one six pound anti-aircraft gun. She was equipped with a four-shaft Bolinder two-cylinder semi-diesel engine with 640 horsepower that allowed a top speed of eleven knots. The monitor's crew consisted of sixty-nine officers and men.