Gillmore’s report
What the guns did, and what weeks of firing did to the guns.
No other Civil War operation put heavy rifled artillery under this kind of sustained strain, and no other officer wrote it up this way. Gillmore's guns fired for weeks at a stretch, from platforms sunk in sand and mud, at ranges no one had used for breaching, and he printed what happened to them.
Nominal weights are a trap in this period. A Parrott is named for the weight of its solid bolt, not for the shell it usually fired, and the same gun appears in the record under two or three descriptions. The bore is the reliable identifier.
6.4-inch bore · about 9,700 lb
The workhorse of the breaching batteries. Cast iron with the wrought-iron reinforcing band at the breech that identifies every Parrott. The common shell ran about 80 pounds; the solid bolt gave the gun its name.
8-inch bore · about 16,500 lb
The heaviest gun in general service before Charleston, and the type mounted in the Marsh Battery. Range enough to reach the city; endurance enough for thirty-six rounds.
10-inch bore · shell about 250 lb
Mounted in Battery Strong against Fort Sumter. The largest rifle Gillmore had, and one of the largest in the field anywhere in the war.
4.2-inch and 3.67-inch bore
The lighter Parrotts held the Folly Island batteries and the parallels — counter-battery work, fire on the beach approach, and support of the working parties rather than breaching.
hexagonal bore · breech-loading
British, mechanically precise, and famous for range. Gillmore treats it as a specialist's weapon rather than a breaching gun: accurate at long distance, but not the instrument for battering a brick wall down.
13-inch, 10-inch and 8-inch
High-angle fire, valuable against troops, field works and anything in the open, and much less effective than officers expected against casemated masonry at long range. Trajectory, fuze and shell weight all mattered, and Gillmore says so.
24-pounder · about 164 lb
Small enough for four men to carry into a trench, which is exactly what it was for. Close-in high-angle fire from the parallels.
25 barrels · .58 caliber
The Billinghurst-Requa volley gun: twenty-five rifle barrels in a frame on a light carriage, loaded from a clip and fired as one volley by a single cap, up to seven volleys a minute. Gillmore put them in the Folly Island batteries, the parallels and the Surf Battery to sweep the beach — one of the war's few operational uses of the type.
semi-steel field rifle
Present in the masked batteries on Folly Island. Wiard's guns were an attempt at a tougher metal than cast iron, and Charleston was the kind of service that found out.
Gillmore went into the campaign already uneasy about his heavy Parrotts — he calls their endurance a matter of some distrust and uncertainty on page 21, before a shot had been fired. The campaign confirmed him. Tubes burst. Vents eroded until they had to be rebushed or the gun abandoned. Carriages strained and platforms shifted in sand that would not stay put. Ammunition varied enough to matter at 4,000 yards.
The theory is in the report too, which is unusual. Gillmore quotes Blakely's argument that in a cast gun the outside metal helps very little unless the strain is properly transmitted from the bore — the reason a large Civil War rifle could be simultaneously powerful and fragile — and prints R. P. Parrott's own defense of his system. The engraved plates of burst Parrotts are the evidence, and they are among the most valuable images in the volume.
That honesty is why the book still matters to anyone who studies the ordnance. Gillmore is not selling the guns. He is reporting what they did in service, including the ways they failed.
Eleven pieces of heavy ordnance were captured with the south end of the island. Gillmore's list includes an 8-inch navy shell gun, 10-inch seacoast mortars, an 8-inch seacoast howitzer, an 8-inch navy gun on a siege carriage, and a Whitworth rifle on a siege carriage. The Confederates had also raised both 11-inch Dahlgren guns from the wreck of the Keokuk that spring and mounted them in the harbor defenses — the heaviest guns they had at Charleston.