A 5.5 inch howitzer.
One of many interesting items from Logan Esarey, ed. Messages and Letters of William Henry Harrison, volume 2. William Henry Harrison goes into a lot of detail about the defenses of Fort Meigs. Counter to what some histories claim, he had only a weak force (mostly the 27th US Infantry, newly recruited in Ohio) with him before several regiments of regulars and militia arrived at his fall-back position at Seneca Town. Note the use of 24-pounder cannonballs recovered from the earlier British bombardment as makeshift ammunition for the two 5.5-inch howitzers present at the Fort.