On March 3, 1862, the Monitor was ready for her next sea trials. Turret turning, guns working, the new crew put her through her paces, steaming around in circles she "turned with helm hard a starboard ...in 4 min 15 sec within a compass of 3 times her length," Master's Mate George Frederickson had written while he stood the afternoon watch. Commodore Gregory, Chief Engineer Garvin and Naval Constructor Hart had come on board to observe this experimental vessel's trial run and to make sure that steering mechanism issues had been resolved.

But testing the new steering mechanism was not the only excitement that day. While the logbook reported that the guns were tested that afternoon, what is not reported is what actually happened during the test firing. As previously noted, the XI-inch Dahlgrens, which were installed in the Monitor's turret each weighed approximately 9 tons, fired a 165-pound shot and were thirteen feet long. Such a gun needs approximately twice its length for recoil room, or twenty-six feet. The turret, however, was only twenty-one feet in diameter.

The gun carriages within the turret were two of a kind, custom made for the Monitor and the Monitor alone. Friction gears tightened with a handscrew served to stop the recoil if operated properly. Unfortunately for Alban Stimers who was to demonstrate the working of the guns, Ericsson had not made the braking mechanisms uniform. As Stimers turned the screw on carriage number one to the right to increase the friction did precisely the opposite and, upon firing, one massive Dahlgren leapt backwards from its carriage and smashed its cascabel into the turret bulkhead.

Assuming erroneously that the second carriage must be a mirror image of the first, Stimers reversed his action and sent the second Dahlgren crashing into the turret bulkhead. Before she had even seen battle, the Monitor had two large dents inside her turret. Those same dents that remain there to this day, and this testament to human error can be seen when the turret's conservation tank is drained.