The writer has long been impressed with the fact that the mode of resistance commonly ascribed to face hardened armor is incorrect. It seems that many have applied to it the theory upon which the development of compound armor was based. That is, the hard face was intended to smash the projectile without allowing penetration; the body and back was to assist the face under impact, and to hold it together even after it had cracked and failed.

Modern improved projectiles are seldom crushed from the point. The point may be fused and abraded or chipped off in breaking up the hard face, but actual disintegration of the projectile only occurs when the resistance that the plate is able to bring on the area of the shell in contact with it is sufficiently great to suddenly check the shell and cause it to break up over its weakest lines through its own inertia. Failure at the point may, however, arise even with low velocities, when the resistance of the plate is less local, provided the energy of the shot is incapable of effecting penetration, or in the case of inferior projectiles.

The usual action of the hard face, however, is that through its inability to bend or flow, it prevents the displacement of the more plastic metal beneath it towards the front, and thus brings the resistance of the whole thickness of the plate to bear before the projectile can advance.

The important retarding influence of the fragments of the hard face carried in by the projectile, is seen in the easier perforation obtained by projectiles whose ogivals are protected by soft steel caps. The cap appears to act as a lubricant or sleeve, covering the asperities of the hardened metal. It is necessary for the cap to be driven into the plate to derive any advantage from it. Doubtless, when thus confined this soft metal transmits pressure as rigidly as the projectile itself, but being capable of flowing, the steel slips through it comparatively unharmed. It is believed that a thicker hardened surface, undulated to prevent or limit flaking, will cause the projectile to carry in sufficient of the hardened face to render the cap incapable of performing the work required of it without increasing its size to a prohibitory extent.

The writer has much for which to thank the officers with whom he has been associated in the Bureau of Ordnance in the way of information. Mr. Millard Hunsiker, now in charge of the manufacture of armor at the Carnegie Steel Company's works, at Homestead, has also kindly placed at his disposal valuable information. He also owes considerable to the Inspectors of Ordnance and officials at the works of the armor makers. These gentlemen are in no way responsible, however, for the conclusions reached. It has been the intention of the writer throughout to avoid discussing those technical details which have been developed by and are the property of the manufacturer rather than the patentee, and by means of which alone the process of face hardening can be made a commercial

success.

SECTION I.

HISTORY AND MANUFACTURE.

Face hardened armor is the direct outcome of efforts to avoid the failures resulting from attempts to temper homogeneous steel plates of sufficiently high carbon to give a very hard face. It is theoretically the perfect armor plate, and doubtless would have been developed long ago had that theory only been enunciated; for the various steps followed in its manufacture, except in certain details, have long been known to the metallurgical world.

Lieutenant Jacques makes the following statement in a recent discussion of the armor problem: "We will not enter here into a discussion of the merits of those who have succeeded in getting their names attached to the various patented methods of surface

hardening, but hope that those who deserve it will get the pecuniary benefit. Ellis treated the first thick plate many years ago; Harvey revived this method, and with the assistance of the Navy Department secured patents which received attention from abroad because of the prominence our Navy Department gave them."

The writer does not believe that Mr. Jacques intends to imply that the Navy Department has the power to obtain or assist to obtain an illegal patent. The assumption that Mr. Harvey revived the Ellis patent is not correct. The old cementation process was carried on usually in cast iron or fire-clay pots at a much lower temperature than that now employed. Had Mr. Harvey proposed merely to cement or convert steel at a temperature above that of molten cast iron, a temperature which would soon have destroyed the old cementation pots, there would still have been considerable novelty in the claim. But Mr. Harvey proposed to do something more by using this high temperature: he proposed to improve the steel, to impart to ingots or other objects of low steel, such as Bessemer steel, the qualities of refined crucible steel! That he succeeded in this, and that his process is in this respect one of a number somewhat akin to it by which inferior steel is improved, must be known to every steel maker. Whether this particular process is essential to the cementation of such high grade material as that of which armor is manufactured, is a different question. It is certain, however, that the Harvey patents cover the process when carried on at that high temperature.

There is an error of minor importance in the article of Lieutenant Jacques above mentioned. The title of Figure "F," Bethlehem 17-in. N-Steel Carbonized, Indiana's Barbettes," is incorrect. Later, in describing Figure "Y," the attack of the same plate by Johnson capped shot, he again speaks of it as carbonized. This was not the case, and its perforation should not be charged against face hardened armor; had the Indiana's 17-inch Barbette plate been face hardened, the premium velocity shot would have smashed on it, as it did on the "Massachusetts " Barbette, instead of perforating it with ease.

The writer has the greatest respect for the energy and ability of Mr. Ellis, but if credit is to be given for the cementation of armor, he must share the honor with others.

We learn in Lieutenant Very's "Development of Armor for Naval Use" that early in 1863 a Mr. Cotchette submitted the following armor proposal to the English Iron Committee: "Upon an armor plate, say 3 inches thick, weld a surface of blistered steel 3/4 of an inch thick; or 'convert,' to a depth of 4 of an inch, the face of an armor plate 31⁄2 inches thick, the plates being subsequently passed through a pair of rolls for consolidation and to reduce the blisters. The face of the plates could then be hardened."

As early as 1867, Jacob Reese, of Pittsburg, Penn., in patenting a cementation compound, proposed cementing and hardening the surface of armor plates. No attempt appears to have been made, however, to carry out his proposition. Ten years later, John D. Ellis patented an armor face hardening process in which a plate wholly of soft iron or having a steely part on either one or both faces had one or both of these surfaces cemented with charcoal in

an ordinary converting furnace. This cementation might be effected either before or after the plate was reduced to its finished size.

In the same year, 1877, the Cammell-Wilson patent was allowed, in which two-fifths of the back of a hard steel plate was decarburized and softened, leaving the face hard and strong. The same firm at this time tempered low steel plates by plunging them in water, which rendered them tougher and more tenacious than when cooled in the air.

In August, 1877, the first Wilson compound plate was tested ; this plate had a steel face and a four-inch wrought iron back.

In 1878, Wilson proposed soldering the steel face to the iron. back by means of tin, zinc, spelter or bronze (a perfectly feasible method, by the way, which may yet be employed to secure thin armor to the ship). This steel face was to be formed of a number of hexagonal or other shaped pieces, in order to localize fractures.

Whitworth, too, proposed, for the same purpose, securing hexagonal plates of very hard steel to a softer back by means of screws.

At the Portsmouth trial of 1888, the "Jessop" plate consisted of a three-inch front cast steel plate, composed of twelve separate pieces of very hard cast steel fastened in a special manner to the seven and one-half inch rear piece of soft cast steel. The theory was that the laminations of the outside plate would localize

destruction and prevent the extension of cracks through the plate. This theory was found to be correct.

Thus far there seemed to be no consideration given to a mean between hard steel, containing about one per cent. of carbon, and which cracked and peeled from the backing, and soft wrought iron, which allowed perforation. The fact that steel could be made sufficiently tough to resist equally as well as compound armor without cracking, although claimed by Schneider, was generally denied by armor makers. No wonder that, under these circumstances, certain authorities made the assertion that physical characteristics had nothing to do with ballistic resistance.

In 1889, the attention of Commander W. M. Folger, U. S. N., the Inspector of Ordnance at the Naval Gun Factory, was attracted by a description of the Harvey process as applied to engraver's plates. At that time it was difficult to obtain steel suitable for gas check disks on account of its cracking in tempering, and Commander Folger concluded to try the Harvey process in obtaining the desired steel. A number of sets of rough steel disks were accordingly Harveyed, machined, and tempered, in a most satisfactory Efforts were then made to Harvey a number of small caliber armor-piercing shell, the manufacture of which, in this country, was meeting with very slight success at that time. This attempt was made by grading the carbon from point to base in a foundation billet of mild steel afterwards forged into a shell. The carbon shell were, however, unable to compete with those containing chromium, and no great success was attained until long afterwards.

manner.

Commander Folger then decided to apply the process to armor by bringing the carbon in the face of a 28 per cent. carbon plate up to a point that would take a chill; the low carbon center and back retaining their softness. In this way he believed that the plate could be uniformly heated and cooled throughout, leaving it, free from structural strains and with the minimum amount of distortion, defects which had been found to be very serious in certain tempered French plates of homogeneous steel. It will be seen that this was really an application of the Ellis process at a temperature higher than that usually employed in cementation.

The first experiment was not a success; the carbon penetrated three inches in depth, far beyond the reach of a true chill; but while