View Full Version : Some armor penetration tests with 15inch Dahlgren gun

12-01-2007, 11:03 AM
I ran across this little bit of fun, and thought it might be enjoyable to see.This shows the power of large bore muzzle loading cannon, and the state of armor technology 140 years ago.

Quote from Treatise on Ordnance and Armor 1865: " If Dahlgren had finally come round to Ericsson’s choice of ironclad design, he also seemed to acknowledge the practical utility of the 15-inch gun. At longer ranges rifled fire became ineffective, and elongated shells frequently toppled in flight while round shot could at least be ricocheted off the water. Against an ironclad, Dahlgren was also convinced from his own testing—and the graphic experience of the Galena in action against Fort Darling (May 15, 1862)—that smashing was better than penetrating.[54] “So long as the present mode of plating continues, there can be little doubt that it will be most effectively attacked by cracking and bending the iron, starting the bolts, stripping off the armor, and breaking away large portions of the wooden structure within.” Though rate of fire was jeopardized by a smoothbore heavier than his own 11-inch gun, Dahlgren had to admit that “it may be conceived that the effects of shells of 330 pounds, and shot of 450 pounds, will be damaging beyond any experience in former battles.”[55] Like the monitors themselves, the gun was at worst an experiment and at best the supreme naval weapon afloat. This was a conclusion Alexander Holley had more or less reached in his monumental contemporary Treatise on Ordnance and Armor (1865):"

12-01-2007, 04:26 PM
Just a few more pics i have gathered, shows technology of that time, (1861-1865.) Along with some other, perhaps later examples.

12-01-2007, 07:22 PM
Very good images and info Tankgeezer :cool:, the crack in the test plate indicate clearly that those are made from cast iron.

12-02-2007, 01:00 PM
Very good images and info Tankgeezer :cool:, the crack in the test plate indicate clearly that those are made from cast iron.
Hi P.K. Certainly could be, I dont know what the plates are made of yet, or whether rolled or cast, but I'm looking into it. This could get interesting.

George Eller
12-02-2007, 03:18 PM

Interesting topic TG :)

The gun emplacement image that you posted above (on the left) is of Federal soldiers with a 100-pounder Parrot gun at Fort Totten.

I have a few images and descriptions of Civil War era naval and coastal guns that I scanned. I would like to get into this more, but will be out for the rest of the day. Hopefully back tomorrow.














12-03-2007, 10:02 PM
Nice scans George, those were interesting times in the gun history, the muzzle loader, smootbore and even some black powder retroloaders were used.

TG, I believe that in those times there was no available the technology to made rolled armor of that thickness.

George Eller
12-03-2007, 10:14 PM
Nice scans George, those were interesting times in the gun history, the muzzle loader, smootbore and even some black powder retroloaders were used.

TG, I believe that in those times there was no available the technology to made rolled armor of that thickness.

Thanks PK :)

Here is more related information:

Ironclad Warship

First Ironclad battles:The U.S. Civil War
http://en.wikipedia.org/wiki/Ironclad_warship#First_Ironclad_battles:The_U.S._C ivil_War

Ironclad armor and construction

The first ironclads were built on wooden or iron hulls, and protected by wrought iron armor backed by thick wooden planking. Ironclads were still being built with wooden hulls into the 1870s, and this was only in part due to the relative cost and scarcity of iron.

Armor and protection schemes

Iron-built ships used wood as part of their protection scheme. HMS Warrior was protected by 4.5 in (114 mm) of wrought iron backed by 15 in (381 mm) of teak, the strongest shipbuilding wood. The wood played two roles, preventing spalling and also preventing the shock of a hit damaging the structure of the ship. Later, wood and iron were combined in 'sandwich' armor, for instance in HMS Inflexible.

Steel was also an obvious material for armor. It was tested in the 1860s, but the steel of the time was too brittle and disintegrated when struck by shells. Steel became practical to use when a way was found to fuse steel onto wrought iron plates, giving a form of compound armor. This compound armor was used by the British in ships built from the late 1870s, first for turret armor (starting with HMS Inflexible) and then for all armor (starting with Colossus of 1882).The French and German navies adopted the innovation almost immediately, with licenses being given for the use of the 'Wilson System' of producing fused armor.


USS Monitor (1862-1862) -- Selected Views


Ironclads and Blockade Runners of the American Civil War

The Technology of the Ironclads


Gunnery tests conducted by both sides early in the war demonstrated that armor thicknesses of two inches or less were insufficient to shield against naval gunfire. On the other hand, it was almost insurmountably difficult to make plating thicker than this, so most ironclads had multiple layers of plate, called "laminated" plating. Two layers of two-inch plate was generally the standard for Southern ironclads; deviations from this usually resulted from lack of iron (as with the Neuse), though a few had a third layer (such as the Tennessee and Columbia). The Monitor had no fewer than eight layers of one-inch plate on her turret. This created problems in fastening the plates together, as it raised the specter of sheared-off boltheads flying around the inside of the turret. This happened in the pilothouse of the Catskill off Fort Wagner, killing the fleet captain of the South Atlantic Blockading Squadron. Plates were usually rolled (cast in oblong blocks and rolled out to their desired dimensions) but on some vessels were actually hammered out (forged plate); this was done to the armor of the New Ironsides, and may partially account for the strength of that vessel's cladding.

All forms of iron armor were highly experimental at the beginning of the war, and several fairly exotic combinations were tried and used. The Galena possessed a complex "rail and plate" system (sometimes misinterpreted to mean T- rails with an outer plate sheathing), assembled in a similar manner to clapboard siding on a house, but it proved vulnerable at Drewry's Bluff. The Keokuk had a weird arrangements of slats of wood interspersed with edge-on iron plates or bars, which proved inadequate at Fort Sumter (she has the dubious distinction of being the only ironclad sunk by gunfire, notwithstanding the Cincinnati, sunk by the Vicksburg batteries; but the latter was hit in her unarmored stern, and was later raised and returned to service anyway). Several of William D. Porter's designs for the riverine ironclads included a layer of rubber or gutta-percha under the iron plates, presumably in the hope that it would help shot rebound off of the armor, but it proved useless and quickly rotted away in the humid Southern climate. Some ships simply used T-rails, despite the recognized fact that they were inferior to rolled plating, though many of the "City" class ironclads supplemented their plate armor with T-rails in certain locations. One cautionary note: some sources refer to ships being plated with "rail road iron," but this does not necessarily mean T-rails. The Albemarle, for example, was armored with rolled plates, but the plates had originally been T-rails, so the ship was often mentioned to be armored with railroad iron. Ships of both sides often had their armor coated with lard or tallow grease in an attempt to deflect shot. The effectiveness of this practice is somewhat arguable, but it would at least have had a positive role in defense against boarding parties, had this ever occurred. The chief result was an often-reported stink as the slush was heated on an iron surface under the blazing Southern sun.

The best armor configuration during the Civil War was found to be the forerunner of composite armor, where several layers of plate were mounted over a solid wooden sheathing, which was the usual method for armoring a Southern ironclad. Had the South possessed enough iron and forging facilities to clad its ships in six or more inches of plate over this sturdy bulkhead, the rams would have proved considerably more formidable. The wood provided a resiliency that the relatively brittle iron plating could not supply.

The original "floating batteries" (Devastation, Lave, Tonnant) used by the French at Sevastopol in 1854 introduced the use of a boxlike armor shield, slightly inclined. Nearly all of the casemated ironclads of the Civil War followed this pattern. Inclined armor is sometimes supposed to have saved weight, but this is a misconception. The volume of iron (and therefore its weight) was still the same, and there was a loss of usable space behind the shield. The advantage of inclined armor lay in the fact that a projectile traveling more or less parallel to the water (direct fire) would strike the shield at a considerable angle of incidence, directing its kinetic energy upward rather than concentrating it fully against the shield. Naturally, this advantage was lost when faced with plunging fire.

As a side note, it is interesting to observe that all monitor turrets were simple right cylinders. This was primarily for ease of construction (Ericsson's original design for the Monitor bore a hemispherical turret, and the turrets on James B. Eads' first-draft plans for the Osage and Milwaukee classes were truncated cones, but all of these were discarded in the final plans). Though vertically-sided, incoming fire that was at all tangential to the turret wall would have been deflected away in the horizontal plane to some extent, giving the monitor turret some of the advantages of the inclined shield without the corresponding loss of space behind the shield or the vulnerability to plunging fire (note that a projectile traveling in a ballistic trajectory has no lateral motion unless deflected in some way). The top of the turret and the monitor's deck, of course, enjoyed no such protection.

One significant weakness of the armoring of all the ironclads was a vulnerability to plunging fire. In the practice of the day, however, direct fire was the norm, so this vulnerability did not often become a significant factor....



George Eller
12-03-2007, 10:15 PM



The rifled cannon was a relatively new development in naval artillery at the time of the Civil War, and many artillerists, John Dahlgren a prime example, maintained that smoothbores were still superior at ordinary ranges of battle, and burst less often than rifles. However, the Union Parrott rifles and Confederate Brooke rifles frequently found their way onto ironclad gundecks. Parrott rifles formed part of the batteries of the New Ironsides, Galena, Roanoke, Onondaga, among others, and nearly every Southern ironclad had 6.4" or 7" Brooke rifles as part of its armament.

Weapons were commonly rated in terms of inches (of the bore of the weapon) or pounds (of the weight of a solid shot). It's not easy to directly compare the two, especially since the weapons measured in inches were usually smoothbores and the weapons rated in pounds were often rifles, usually with enlongated projectiles. Dahlgren pieces were usually named with the Roman numeral of the caliber (for example, XI-inch for 11", and XV-inch for 15"). Also, there was disparity between Army and Navy nomenclature; the weapon that the Union Navy called a 150-pounder was named a 200-pounder in Union Army service (the typical weight of the shell fired by this piece was in fact 152 pounds)...

...Rifles had significant advantages over smoothbores in range, accuracy, and penetrating power, though their projectiles could not be skipped over the water, and they had a tendency to bury themselves in the ground, reducing the shell-blast effect. The big 15" Dahlgren smoothbores mounted on most monitors were devastating at close range, able to penetrate the heaviest-armored Southern ironclads, but their effectiveness dropped off rapidly with distance. Eventually, of course, the rifle completely replaced the smoothbore in naval artillery.

The most important pieces of Union naval ordnance were the 11" Dahlgren smoothbore (used in the Monitor, New Ironsides, Keokuk, the Passaic, Osage, Milwaukee, and Sandusky classes, along with the failed Casco class); the 15" Dahlgren smoothbore (used in the Passaic, Canonicus, and Monadnock classes, the Dictator, and the never- completed Dunderberg and Kalamazoo class ships); and the 100- and 150- pounder Parrott rifles. Southern ironclads, as previously mentioned, usually bore various sizes of Brooke rifles, but many had a hodgepodge of other weapons, mostly acquired at the fall of the Gosport Navy Yard at Norfolk....

...Solid shot, particularly of the few conical steel-tipped varieties, was the precursor of modern armor-piercing shot. When propelled by a sufficient powder charge, they could and did penetrate ironclad armor. Solid shot was also effective against stone or masonry fortifications, but mostly ineffective against earthworks; if a shot hit such a fortification squarely, it would tend to burrow in and stay there, basically making the earthworks stronger. ...

...The most effective method of mounting guns, of course, was the monitor turret, an armored rotating gun platform that allowed the guns to fire at nearly any angle, regardless of the bearing of the ship. Ericsson's ideal was a complete 360° field of fire, but this was never attained in any completed vessel. The original Monitor could not fire directly forward, since the pilothouse was in the way, and every successive design had permanent smokestacks, deckhouses, or even other turrets blocking a portion of the field of fire. Nevertheless, the flexibility in aiming a monitor's guns gave it an important advantage against vessels mounting fixed broadside or pivot guns. To be sure, there were other problems. The limited space inside a monitor turret made it impossible for the guns to roll backward with the recoil in the usual manner, so there was special mechanical friction gear to absorb the recoil, requiring the gun crew to set this gear lest the guns jump their carriages upon firing. The engine power used to turn the turret was a little different in the various monitor classes, so the turrets turned at different rates and some were not accurate enough to stop on a precise bearing; in fact, the Monitor's own turret engine was so inaccurate that the turret crew began firing "on the fly" without stopping the turret, and eventually left the turret stationary and let the ship's motion bring the target into view. This somewhat defeated the purpose of the turret. However, successive classes improved on this situation.


Dahlgren gun
Specific Shell and Related Guns
Table of Dahlgren Shell and Related Guns
http://en.wikipedia.org/wiki/Dahlgren_guns#Table_of_Dahlgren_Shell_and_Related_ Guns


Civil War Artillery Projectiles
By Jack W. Melton, Jr. & Lawrence E. Pawl
Tables of Shot Information for Smoothbore Guns, Stands of Grape & Canister
Tables for Cannon & Artillery Projectiles
Rifled Artillery Projectiles
Spherical Artillery Projectiles


12-04-2007, 11:06 PM
If the armor was of Wrought iron, it had to be either rolled, or hammered. as it isnt possible to cast it.(wrought structure is destroyed if melted.) But that isnt to say cast iron was not employed,I just dont have any source authority to cite A popular and time honored method of producing large pieces of wrought iron for shafts, or plates was to stack, and bind plates of iron much like laminating planks of wood. Once these individual plates were wired together, they were placed by means of a gib, into a funace, heated to welding temperature, and then withdrawn, and put to the tender care of a large steam hammer. this working would weld all of the pieces together as one large part, and when completed, could be finished to final size beneath the hammer, and be ready for machining, and use.
Wrought Iron is extremely resilient, and strong in tension.The only drawback as armor plate is that if exposed to steady, and constant hammering when cold, the laminal structure of the metal will eventually begin to separate.This can be seen sometimes in the iron tires of wagon wheels after years of hitting rocks on the roads.
I know that rolling machines were extant during the 1860's, but i dont know the capacities of these machines. Some later(1863,1865) 3inch guns were produced by rolling wrought iron on a mandrel, and the inserting a breech plug of steel, and after heating to welding temps, was rolled to weld the chase,and seal the plug.Again, I dont remember the actual capacity of the machine.