Rodman gun refers to a series of
American Civil War-era columbiads designed by Union artilleryman Thomas Jackson Rodman [" [http://www.cwartillery.org/afammen.html Thomas Jackson Rodman] ", Confederate Artillerymen, The Civil War Artillery Page. Retrieved 12-20- 2007.] ( 1815– 1871). The guns were designed to fire both shot and shell. These heavy guns were intended to be mounted in seacoast fortifications. They were built in 8-inch, 10-inch, 13-inch, 15-inch, and 20-inch bore. Other than size, the guns were all nearly identical in design, with a curving soda bottle shape, large flat cascabels with ratchets or sockets for the elevating mechanism. Rodman guns were true guns that did not have a howitzer-like powder chamber, as did many earlier columbiads. Rodman guns differed from all previous artillerybecause they were hollow cast, a new technology that Rodman developed that resulted in cast ironguns that were much stronger than their predecessors.
Guns had been traditionally cast solid and the bore was bored out of the solid metal. With this traditional method, the gun cooled from the outside inward. Castings shrink as they cool. As each succeeding layer cooled it contracted, pulling away from the previously cooled metal creating voids and tension cracks. Rodman devised a method of casting where the gun cooled from the inside out, so that as cooling occurred, it created compression rather than tension. This resulted in a much stronger gun.
With Rodman’s method of casting, a cooling core was placed in the mold before casting. This core consisted of a watertight cast iron tube, closed at the lower end. A second, smaller tube, open at the bottom was inserted into the first. As the molten iron was poured into the mold, water was pumped through the smaller tube to the bottom of the larger tube. The water rose through the space between the two tubes and flowed out at the top. The water continued flowing as the metal cooled. To further ensure that the gun cooled from the inside out, a fire was built around the iron flask containing the gun mold, keeping the gun mold nearly red-hot. For an 8-inch Rodman
columbiad, the core was removed 25 hours after casting and the flow of water continued through the space left by the core for another 40 hours. Over 50,000 gallons of water was used in the process. For larger guns, the cooling periods were longer and more water was used.
After cooling the gun the machining process began. The bore was bored out proper size, the exterior was turned smooth, the trunnions were turned on a trunnion
lathe, and a vent was drilled.
Columbiads were not the only guns cast using Rodman’s method. Dalgren XV-inch shell guns for the
U.S. Navywere also hollow cast. A 20-inch hollow cast gun, which may not have been identical to the two guns supplied to the U.S. Army, was sold to Peru.
Rodman guns were cast at the
Fort Pitt Foundry, Pittsburgh, Pennsylvania; the Scott Foundry, Reading, Pennsylvania; Cyrus Alger & Co., Boston, Massachusetts; and the West Point Foundry, Cold Spring, New York.
Rodman guns were all nearly identical in design, with a curving soda bottle shape, the only differences being the size of the gun. They were all
smoothboreguns designed to fire spherical shot and shell, primarily against ships. The guns were elevated and depressed by means of a levercalled the elevating bar. The point of this lever fits into ratchets on the earliest guns cast, or sockets on the later guns. The fulcrum, called the ratchet post, fit on the rear transom of the upper carriage. The ratchet post was cast iron and had several notches for adjusting the position of the elevating bar.
Only one 13-inch Rodman gun appears to have been made, but it was placed in service Harv|Ripley|1984|p=79. The two 20-inch Rodman guns were emplaced at
Fort Hamilton, New York. The other Rodman guns were placed in seacoast fortifications around the United States. It took 8 men to load and fire a 10-inch Rodman gun, and 12 men for a 15-inch Rodman gun.
Over 140 Rodman guns survive today and they may be seen at coastal fortifications around the country.
Carriages for Rodman Guns
Rodman guns were mounted on three type of carriages-- a front-pintle barbette carriage, a center-pintle barbette carriage, and a casemate carriage. All of these carriages were made of
wrought iron. All three types of carriage were similar in design having an upper carriage that was paced on a two rail chassis. The gun and upper carriage recoiled along the chassis. The chassis would pivot to train the gun left or right.
The barbette carriages were designed to fire over a [http://civilwarfortifications.com/dictionary/xgp-016.html parapet] and could be used in either permanent or temporary fortifications. The front pintle carriage pivoted at the front of the chassis. This made the gun mount more compact and allowed the gun and detachment to be better protected by [http://civilwarfortifications.com/dictionary/xge-001.html embrasures] and [http://civilwarfortifications.com/dictionary/xgt-007.html traverses] . The center pintle carriage gave the gun a 360° traverse and was stronger for guns firing at high angles because the pintle, the strongest part of the carriage, would have been under the breech when the gun was fired at high angles.
The casemate carriage was designed to fire from [http://civilwarfortifications.com/dictionary/xgc-006.html casemates] which were chambers in permanent fortifications. The carriage was essentially a front-pintle design, with the pintle fixed in the masonry in front of the chassis and below the guns [http://civilwarfortifications.com/dictionary/xge-001.html embrasure] . A “tongue’’ connected the chassis to the pintle. The casemate carriage has a lower profile than the than the barbette carriages.
The 8-inch and 10-inch Rodman guns could be mounted on all three types of carriages. The 15-inch Rodman guns were mounted on both types of barbette carriage. The two 20-inch guns were mounted on front-pintle barbette carriages.
Rodmans in Action
Rodman guns saw little, if any action during the Civil War. Two 10-inch columbiads were used in 1864 and 1865 in Union operation against
Fort SumterHarv|Suter|1891|p=117. It seems likely, due to the time period in which they were used, that these were Rodman guns rather than earlier model columbiads. Other reports of the use of 8-inch and 10-inch columbiads may refer to Rodman guns. The 15-inch Rodman guns were never fired in anger Harv|Birkhimer|1884|p=291,fn. The 20-inch Rodmans were only fired eight times in practice Harv|Ripley|1984|p=80.
During the War, and immediately after, attempts were made to cast rifled Rodman guns. Unsuccessful attempts were made to cast a 12-inch rifle in 1861, an 8-inch rifle in 1862, and another 12-inch rifle in 1868 Harv|Birkhimer|1884|p=267. In the 1870’s and 1880’s efforts focused on converting existing Rodman guns into rifles. 10-inch Rodman smoothbore guns were converted into 8-inch rifles. The first method used was inserting a wrought iron rifle sleeve through the muzzle, a similar steel sleeve was also used later. The last method involved drilling and tapping the breech of the 10-inch Rodman and inserting a rifled steel sleeve and screwing it in tight with a threaded breech plug. These breech inserted guns are easily recognized by the square “
cascabel” which was designed to provide purchase for screwing the breech plug and liner securely into the gun.
These conversions were not viewed favorably, were primarily seen as cheap stopgaps until modern
breech-loadingrifles could be developed and emplaced Harv|Birkhimer|1884|p=293.
Joseph R. Andersonof the Tredegar Iron Works, Richmond, Virginiaand Junius L. Archerof the Bellona Foundry, Midlothian, Virginia(the only two gun foundries then operating in what would become the Confederacy) failed to adopt the Rodman technique of hollow casting, and as result the U.S. Armycancelled contracts with both firms for casting columbiads. Therefore at the outbreak of the war, southern foundries were not capable of casting guns using the Rodman method Harv|Daniel & Gunter|1977|p=vii.
The Confederates did solid cast 8-inch and 10-inch columbiads that resemble Rodman guns. A closer examination of these Confederate columbiads reveals that they have a straighter cylindrical contour between the trunnions and the breech as opposed to the sweeping continuous curve of the Rodman gun. The Confederate columbiads have longer trunnions that were intended for use with heavy wooden carriages. The Union gun were designed to be mounted in iron carriages with thinner cheeks, permitting shorter trunnions. The exteriors of the Confederate columbiads are rough, not having been finished on a lathe as were their Union counterparts.
On November 14, 1864, and February 20, 1865, Anderson cast two 12-inch columbiads using the Rodman method at the
Tredegar Iron Works. The guns were made too late and were never finished or mounted Harv|Daniel & Gunter|1977|pp=vii,103,104.
Misnamed as Rodmans
The 3-inch ordnance rifle and the 4.5-inch siege rifle were frequently misidentified as Rodmans. Neither gun was hollow cast. The 3-inch ordnance rifle was made of hammer welded wrought iron and the 4.5-inch siege rifle was conventionally cast.
first =William E.
title = Historical Sketch of the Organization, Administration, Matérial and Tactics of the Artillery, United States Army
place =Washington, D.C.
publisher =James J. Chapman
url = http://www.archive.org/details/historicalsketch00birkrich
first =Larry J.
first2 =Riley W.
title =Confederate Cannon Foundries
place =Union City, Tennessee
publisher =Pioneer Press.
author-link =John Gibbon
title =The Artillerist's Manual
place =New York
publisher =D. Van Nostrand .
author-link =Josiah Gorgas
title =The Ordnance Manual for the Use of the Officers of the Confederate States Army
place =Richmond, Virginia.
title =Artillery Through the Ages: A Short Illustrated History of Cannon, Emphasizing Types Used in America
place =Washington, D.C.
publisher =Government Printing Office
title =Artillery and Ammunition of the Civil War
place =Charleston, S.C.
publisher =The Battery Press
first =Charles R.
title =Report from Hilton Head, S.C., June 8, 1864
journal = The War of the Rebellion: A Compilation of the Official Records of the Union and Confederate Armies, Series I.
publisher = Government Printing Office
location =Washington, D.C.
first =John Caldwell
title =Manual of Heavy Artillery Service: For the Use of the Army and Militia of the United States
place =Washington, D.C.
publisher =James J. Chapman
* [http://www.cwartillery.org/artillery.html The Civil War Artillery Page]
* [http://www.civilwarartillery.com Civil War Artillery Projectiles]
* [http://civilwarfortifications.com/index.html Civil War Field Fortifications Website]
* [http://earthstation9.com/index.html?1876_phi.htm The World's Fair and Exposition Information and Reference Guide: 1876 US Centennial Exhibition]
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