The US Army 42-Pounders of USS Cairo

Oct 5

US Army 42-Pounder Seacoast Gun, Pattern 1831, displayed aboard USS Cairo

The forward-firing armament of USS Cairo is two rifled US Army 42-Pounders, Pattern 1845, and a US Navy 8-Inch shell gun of 63 hundredweight. Additionally, there is a US Army 42-Pounder, Pattern 1831, as the forward gun on the starboard broadside.

The bow 42-Pounders as originally manufactured weighted 8,359 pounds and 8,397 pounds. They were both cast at Fort Pitt Foundry in 1856. Elizabeth Joyner's book on USS Cairo gives their Registry Numbers as Fort Pitt No. 28 (port) and Fort Pitt No. 20 (starboard). (Note, Olmstead et al. gives the registry numbers as 8 and 20. My photos do not show the muzzle faces in enough detail to tell, but I follow Joyner's numbers as the specialized work on the subject.)

The forward starboard gun is a US Army 42-Pounder Seacoast Gun, Pattern 1831. Like the Army 32-Pounders of 1829, this 42-Pounder has a loop above the cascabel for a breeching rope, an unusual feature for a cannon designed for use ashore. As manufactured, it weighed 8,582 pounds. It was cast at Columbia Foundry in 1837.

All three 42-Pounders were originally smoothbores but had been rifled for service in the American Civil War. Originally firing a 7-Inch, 42-pound round shot, as rifles they were capable of firing much heavier projectiles. Upon recovery, two of the 42-Pounders were found to be loaded with 87 pound explosive shells. A similar shell may be seen among the display of projectiles in adjacent museum.

While rifling a smoothbore gave a cannon increased accuracy and hitting power, the improvements came at the cost of much greater strain on the piece. Not only was the cannon now firing projectiles twice as heavy as designed, but rifled projectiles were designed with a base which expanded on firing (or some other means of engaging the rifling). This meant that the gases which would pass around the windage of a round ball would not do so in a rifle. Rifled smoothbores, unless given an wrought iron reinforcing band, were seen as being of greater risk of bursting than other types.

The center bow gun, a US Navy 8-Inch shell gun of 63 hundredweight, was cast by Fort Pitt Foundry in 1845. It is marked as weighing in hundredweight 64-0-26 (7,194 pounds). It is US Navy Registry Number 368. The 8-Inch 63cwt is a smoothbore designed to fire a 51-pound explosive round shell. The museum also shows a stand of grape and a canister round for the 8-Inch guns aboard Cairo.

The mix of army and navy guns aboard may reflect the origin of Cairo and her sisters as a project of the army. USS Cairo's sister ships which survived later in the war seem to have had the forward firing armament replaced. Three 9-Inch Dahlgrens seem to have been typical. On the other hand, USS Cairo, sunk in 1862 and raised 100 years later, preserved a number of cannons which were borderline obsolescent in 1862 and were not types kept for future service after the war.