U.S.S. CairoEngine & Boilers

A National Historic Mechanical Engineering LandmarkPhoto by Tom Roster

The U.S.S. Cairo and Museum, Vicksburg National Military Park

Vicksburg, MississippiJune 15, 1990

The American Society of® Mechanical Engineers

National Historic

Mechanical Engineering Landmark

U.S.S. Cairo Engine and Boilers1862

THE CAIRO IS THE SOLE SURVIVOR OF THE FLEET OFRIVER GUNBOATS BUILT BY THE UNION DURING THECIVIL WAR WITH THE OBJECT OF CONTROLLING THELOWER MISSISSIPPI RIVER. DESIGNED BY SAMUELPOOK AND BUILT BY JAMES B. EADS, THE 175-FT.IRONCLAD VESSEL HAD 13 GUNS. THE PROPULSIONSYSTEM IS THE ONLY KNOWN EARLY EXAMPLE OFTHE WIDELY USED “WESTERN RIVERS” STEAMBOATENGINE, CHARACTERIZED BY MULTIPLE FIRE-TUBEBOILERS WITH SHARED STEAM AND MUD DRUMS,AND A TWO-CYLINDER, NON-CONDENSING ENGINEHAVING A SMALL BORE, LONG STROKE, AND POPPETVALVES. THIS WAS DESIGNED BY A. T. MERRITT. WITHA 22-IN BORE AND 6-FT STROKE, IT DEVELOPED ABOUT600 HORSEPOWER AND DROVE A SHELTEREDPADDLEWHEEL OF 22-FT DIAMETER AND 15-FT WIDTH.

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS—1990

Historical Significance

The only known photograph of theU.S.S. Cairo, taken early in 1862while she was being outfitted atCairo, Illinois.

The engine and boilers of the U.S.S. Cairo,recovered in December 1964 when the CivilWar gunboat was raised from the YazooRiver in Mississippi, are of a design typicalof those used for riverboats steaming the“western waters” in the mid-1800s.

Tough, reliable, and simple to operate—though at times guilty of unexpected explo-sions—these mechanical wonders openedthe lands to development along the Missis-sippi River and its major tributaries.

When war broke out between the Northand the South in 1861, control of the Missis-sippi River was of critical concern to bothcombatants, and boats driven by this samereliable machinery helped to determine theoutcome. One of these was the U.S.S. Cairo.

The U.S.S. Cairo, an ironclad gunboat,was one of seven “city class” gunboatsdesigned by the naval constructor, SamuelM. Pook, for the Union Army in order totake control of the lower Mississippi Riverfrom the Confederates.

The engine and boilers were designedby A. Thomas Merritt, a civilian engineerfrom Cincinnati, Ohio, and built by theHartupee Company of Pittsburgh, Pennsyl-vania. Merritt also served as superintendentof construction of the vessels.

James B. Eads, a civilian engineer fromSt. Louis and an experienced river boatbuilder, was awarded a contract August 7,1861, by the U.S. Army to build the gun-boats. The Cairo, named after Cairo, Illinois,was built in the Marine Railway and ShipYard at Mound City, Illinois, and was com-missioned January 15, 1862.

The Cairo’s first captain was LieutenantNathaniel C. Bryant. The boat took part inmissions on the Ohio, Cumberland andTennessee rivers before going down theMississippi River and engaging in its firstcontest May 10 off Plum Point above FortPillow, Tennessee, a Confederate strongholdguarding the river approaches to Memphis.During the summer of 1862, the Cairo pa-trolled the waters north and south of con-quered Fort Pillow, engaging in little activity.

Due to Lieutenant Bryant’s failing health, heturned his command of the gunboat over toLieutenant Commander Thomas O. SelfridgeJr. on September 12. In late 1862, the Cairowas ordered to participate in another attemptby the Union to capture Vicksburg. One ofher assignments was to help clear the YazooRiver up to Greenwood, Mississippi.

On the morning of December 12, accom-panied by the tinclads Marmora and Signal,the ram Queen of the West, and the ironcladPittsburg, the Cairo made its way up theYazoo River with the Marmora leading theway. Sixteen miles up the Yazoo River, Com-mander Selfridge, hearing small arms fire,believed his flotilla was under attack andordered the Cairo ahead into unrecon-noitered waters. Within minutes, two Con-federate torpedoes (mines) exploded underthe Cairo, sinking it within twelve minutes.The mines were connected to a battery cellon the shore, which detonated the mine.This was the first craft ever sunk by an elec-trically detonated mine.

After laying on the bottom of the muddyYazoo River for more than 100 years, theCairo was raised in December 1964. Hermajor contribution to history lies in herpreservation of firsthand information on thetype of gunboats and their propulsion sys-tems used for river operations in the CivilWar, and of the details of boat life lived bythe crewmen on board.

Although considerably damaged duringthe lifting operation, the boat was substan-tially restored and made available to thepublic for viewing. The Cairo was restoredby the National Park Service and can be seenat the Vicksburg National Military Park.Artifacts for the Cairo are on exhibit at theadjacent U.S.S. Cairo Museum. The engineand boilers are restored within the Cairo.

Illustrations courtesy of the National Park Service.

U.S.S. Cairo, restored—VicksburgNational Military Park

Wood and iron pitman arms on eachside of the Cairo served as connectingrods between steamdriven enginesand paddle shaft cranks.

Technical BackgroundThe U.S.S. Cairo is the only surviving exam-ple of a class of warships specifically de-signed for use on the Mississippi Riverduring the Civil War. The Cairo’s engine andboilers are among the oldest and best surviv-

either end by cranks mounted 90 degrees toeach other. The two rudders were located afton each side of the raceway to steer the gun-boat.

The ironclad was equipped with fivefire-tube boilers, each 36 inches in diameterand 25-feet long, with five 7 1/2-inch flues

Sectional view of the U.S.S. Cairoing examples of typical engines designed forboats plying the “western rivers.”

The reciprocating steam engine was theuniversal prime mover in self-propelledcraft during that era. All of these engineswere simple, single-expansion, and eithercondensing or non-condensing. The differ-ent types of engines were labelled accordingto the position of the cylinders—vertical,horizontal, or inclined. The engine positionmatched the type of paddle wheel used topropel the boat. Vertical or inclined engineswere used to drive the side wheel types. Astern wheel would be driven by a horizontalor an inclined engine, with the latter beingmore desirable for a gunboat, since the en-gine would be under the water line.

Similar to the stern wheel, the Cairo’srecessed paddle wheel was located withinthe protected raceway, between the case-mates to protect it from enemy fire. Theiron shaft of the paddle wheel was driven at

inside each boiler. The sides of the boilersare 5/16-inch thick, with heads 12/16-inchthick. The boilers operated at 140 poundsper square inch steam pressure. Instrumen-tation installed on each set of boilers was asteam gauge and a water gauge. The cast-iron fire fronts fit to the front of the boilerwith a five-foot-long firebox. It consumed 18to 20 bushels—approximately 1,980pounds—of coal per hour. The bed of thefirebox was lined with fire brick and en-closed in good sheet iron. Located under theforward section of each boiler, it suppliedhot gasses to the boilers by routing the gasaft and under the boilers and into the aft fluemouths of the boilers. The flue gas wasdrawn forward through the flues and drawnup the tall stack by natural draft. Placed onthe front end of the boilers were two smokestacks, 44 inches in diameter and 28 feet inheight.

Two mud drums, which supported theboilers and collected sediment of thepumped feed water, were connected to thebottom of the boilers. One was located closeto the after end of the boilers with stopvalves for supplying the boilers with water.The other mud drum was located immedi-ately aft of the firebox, but without watersupply connections. At one end of this drumwas a blow-off valve to drain the boilers.

Steam was carried from the boiler to thesteam drum. Located in the rear of the boil-ers, it served as a collector and manifold.Each connection pipe to the drum had astop valve to cut off steam flow to the drumand, more importantly, to the engine. Con-nected to the after side of the center of thesteam drum, was a steam pipe carryingsteam to the main steam engine, steam-driven capstan and auxiliary engine.

The Cairo was equipped with a two-cylinder non-condensing, reciprocatingmain steam engine. The cylinders, mountedat a 15-degree angle, were made of cast-ironwith a 22-inch bore and were of a length toaccommodate a 72-inch stroke. On one sideof the cylinder at each end was a supplynozzle with an opening of 9 inches by 4inches, with a flange 15-inches square by1 1/4-inches thick, for receiving steam. On the

U.S.S. Cairo engine before restoration

U.S.S. Cairo engine after restoration

other side of the cylinder were two similarnozzles for steam exhaust from the cylinder.The cast-iron piston, with a 4-inch space forpacking, was attached to a wrought ironpiston rod which was 4 inches in diameterand 110-inches long. The engine exhauststeam heated water in the preheater, andthen exhausted to the stack.

A one-cylinder auxiliary engine, alsocalled “the doctor” because it cured the illsof the steam boat, was used to drive twocold-water pumps and two main forcepumps to supply the boiler with water,drawing it from the river. The cylinder wasmade of cast-iron with a diameter of 8 inchesand a length to accommodate a 21-inchstroke. The cast-iron piston, which was 5-inches deep and fitted with metallic packingrings, was attached to a piston rod whichwas 1 3/4-inches in diameter and 3-feet long.Steam ports were one-half inch by 2 inchesand the exhaust port was 1-inch by 2-inches.The steam chest was one-half-inch thick.The Cairo doctor was lost during the salvage,but was traditionally located aft of the boilersbetween the cylinders of the main engine.

The cold-water pumps sent water intothe preheater where the water was heated

by exhaust steam from the main engine. Themain force pumps sent the heated water intothe aft mud drum and to the boilers.

Robert M. Shepard IIIASME Mississippi Section

Landmark Ceremony Committee

Bibliography

Bearss, Edwin C., Hardluck Ironclad, The Sinking andSalvage of the Cairo, revised edition, Louisiana StateUniversity Press, Baton Rouge, 1980

Gosnell, Allen H., Guns on the Western Waters, LouisianaState University Press, Baton Rouge, 1949

Jones, Virgil Carrington and Peterson, Harold L.,U.S.S. Cairo, The Story of a Civil War Gunboat, a bookletpublished by the National Park Service, U.S. Depart-ment of the Interior, 1971

The War of the Rebellion: A compilation of the OfficialRecords of the Union and Confederate Armies, Washington,D.C., 1880-1901—Series III, Volume II, pages 820-832(engine specifications)

McGrath, Tom and Ashley, Doug, Historic StructuresReport: The U.S.S. Cairo, a booklet published by theNational Park Service, U.S. Department of the Interior,1981 (drawing of the engines and boilers)

The History and HeritageProgram of ASME

The ASME History and Heritage Recog-nition Program began in September 1971. Toimplement and achieve its goals, ASMEformed a History and Heritage Committee,initially composed of mechanical engineers,historians of technology, and the curator ofmechanical engineering at the SmithsonianInstitution. The committee provides a publicservice by examining, noting, recording,and acknowledging mechanical engineeringachievements of particular significance. TheHistory and Heritage Committee is part ofthe ASME Council on Public Affairs andBoard on Public Information.

The U.S.S. Cairo engine and boilers arethe 96th National Historic Mechanical Engi-neering Landmark to be designated. Sincethe ASME Historic Mechanical EngineeringProgram began, 136 Historic MechanicalEngineering Landmarks, five MechanicalEngineering Heritage Sites, and one Me-chanical Engineering Heritage Collectionhave been recognized. Each reflects its influ-ence on society, either in its immediate lo-cale, nationwide, or throughout the world.

An ASME landmark represents a pro-gressive step in the evolution of mechanicalengineering. Site designations note eventsor developments of clear historical impor-tance to mechanical engineers. Collectionsmark the contributions of a number of ob-jects with special significance to the histori-cal development of mechanical engineering.

The ASME Historic Mechanical Engi-neering Recognition Program illuminatesour technological heritage and serves toencourage the preservation of the physicalremains of historically important works. Itprovides an annotated roster for engineers,students, educators, historians and travelers,and helps establish persistent reminders ofwhere we have been and where we are goingalong the divergent paths of discovery. Formore information, please contact the PublicInformation Department, American Societyof Mechanical Engineers, 345 East 47thStreet, New York, New York 10017, (212)705-7740.

The American Societyof Mechanical Engineers

Arthur E. Bergles, P.E., PresidentGary D. Smith, Vice President, Region XIJ.L. Lee, P.E., History & Heritage Committee Chair-man, Region XIR. Stephen Schermerhorn, P.E., Senior Vice President,

Public AffairsGeorge A. Jacobson, Vice President, Public Information

David L. Belden, P.E., Executive DirectorDavid R. Cook, P.E., Director, South Regional Office

The ASME National History &Heritage Committee

Euan F.C. Somerscales, ChairmanRobert M. Vogel, SecretaryRobert B. GaitherRichard S. Hartenberg, P.E.J. Paul Hartman, P.E.J.L. Lee, P.E.John H. LienhardJoseph P. Van Overveen, P.E.R. Carson Dalzell, Chairman EmeritusCarron Garvin-Donohue, Staff LiaisonDiane Kaylor, Manager, Special Projects

The ASME Mississippi Section

Stan Prather, ChairmanRonald S. Kimbrough, Vice ChairmanGregory J. Chancellor, SecretaryAndrew C. Taylor, Treasurer

National Park Service

William O. Nichols, Superintendent,Vicksburg National Military ParkRobert M. Baker, Regional Director,Southeast Regional OfficeJames M. Ridenour, DirectorEdwin C. Bearss, Chief Historian

Landmark Ceremony Committee—Mississippi Section

Malcolm A. Allred Stan PratherJames L. Campbell Ram A. SharmaJ. Larry Hartness Pete Shead

Peggy Jeanes Robert M. Shepard III

B. Stan Merritt Andrew C. TaylorW. Lamar Nail Jr. Steven E. ThomasKeith J. Orgeron, Chairman Paul Young