During the Civil War, one of the biggest threats for plantations along the Rappahannock River was the Union Gunboats that patrolled the waterway.
According to Wikipedia:
“A gunboat was usually a small undecked vessel caring single smoothbore cannon in the bow, or just two or three such cannons. A gunboat could carry one or two masts or be oar-powered only, but the single-masted version of about 15m (49ft) length was most typical.
