The 13-inch seacoast mortar weighed over 17,000 pounds and, as its common name implies, was intended for siege and fortifications and not field work.
Siege of Petersburg
This monster was made portable during the Siege of Petersburg by being mounted on a railroad car, specially strengthened with extra beams and iron rods to withstand the strain of firing.
Since this mortar threw a 218 pound shell about two and one-half miles with a charge of 20 pounds of powder, this strain was considerable.