When and how did steel supplant iron for artillery?

The story that you are looking for is laid out in The Arms of Krupp, by William Manchester. It begins in the 1850's when Alfred Krupp built his industrial empire on the sale of rail stock, and his patented, seamless rail tire. Krupp was obsessed with the idea of steel ordnance, and devoted a significant amount of resources to its development from the earliest times. Kaiser Bismarck was fully aware of its potential, and the two forged a close relationship. This began the ascendance of the Krupp family in German business and politics.

The first use of steel ordnance with devastating results was the Franco Prussian war of 1870. The Germans also made highly effective use of railroads. The Battle Sedan, and the siege of Paris were stunning examples of the superior artillery.

Before the war, The Krupp factory had begun its conversion from the Bessemer process to the Siemens-Martin process, which continued over the next decade. The 1880's were the beginning of the European arms race for steel ordnance. The Reich remained the first obligation of the Krupp concern, but it began to export ordnance all over Europe and the world. Its priority was profit, and it even sold to Prussia's enemies with embarrassing results.

The shift from iron to steel for big guns began in 1847. That's not when the militaries adopted it of course. But the idea, the process and the prototype began at that time.

Alfred Krupp and his competitor Jacob Mayer were the first to cast steel into this form. With Mayer being the now less known but more innovative part for steel casting.

They stole this concept from the English and applied it to new dimensions. The Prussian military was moderately enthusiastic, but declined to pay the price demanded.

People in general didn't grasp the advantages that quickly, just like Martin von Wahrendorff's innovations.

In the light of these high-minded goals, one of Krupp’s most eye-catching exhibits served as a distinct shock. “The English will have their eyes opened,” he wrote to the “Collegium” or “directory board” in 1851. Krupp displayed a highly polished and exceedingly shiny cannon, set next to an officer’s armor with an elegant orange-yellow silk lining. The Illustrated London News referred to “the beautiful steel cannon.”27 Many comments focused in a similar vein on the aesthetics rather than the technical characteristics of the cannon.

A decisive part of the advance in artillery technology in the 1860s, the development of barrels constructed by means of nested rings of tubes, which greatly enhanced the strength and resilience of the cannon bore, came at the insistence of Russian military procurement.

The Prussian state had its own logic and its own traditions, and indisputably the best way to capture the imagination of the Prussian state and its agents was to supply military equipment. In 1843 Krupp sent a cast-iron rifle barrel to Lieutenant von Donat, explicitly arguing that the success of the rifle amounted to “a demonstration in miniature of the suitability of this material for the manufacture of cannons.” By 1844 he was addressing Minister of War von Boyen with an appeal to replace wrought iron in rifle barrels and bronze cannons with cast iron. The ministry sent a drawing for a new cannon, and in 1846 Krupp produced a model. By August 1847 he was sending a 7.5 cm piece, but it seems to have excited little interest, and it was not tested by the Prussian military. In consequence, Krupp seriously contemplated sending the artillery piece to Paris in the summer of 1848, where street fighting meant that there was an obvious need for military equipment. The revolutions of 1848 doubtless heightened the appreciation of the state authorities for military production. After all, social order now seemed to depend on the bayonet. In June 1848, Krupp wrote laconically to a former representative of the firm about the poor state of business: “My brother in Vienna is making not spoons—but weapons.” In fact the Berndorf factory had converted itself from spoons to sabers. At the Crystal Palace in London, the real engineering feat lay in

_{Harold James: "Krupp: A History of the Legendary German Firm", Princeton University Press, 2012.}

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1847 Prussia receives Alfred’s first steel cannon.

Prussia was approached first. On the hottest Sunday of that summer he brushed and mounted his finest horse and rode over to the Saarn arsenal. This opening move was unpropitious. Saarn’s sweating guard was rude; Alfred was turned away. Calling again, he learned that the officer on duty, a Lieutenant von Donat, thought the idea of steel weapons rather funny. However, von Donat intimated that a brother officer, a Captain von Linger, might feel otherwise. The lieutenant, one gathers, regarded the captain as something of an eccentric. Unfortunately, the armory’s non-conformist was absent. Doubtless this explanation had been offered to let Alfred down easily, but he galloped back and dispatched his best gun to Saarn. In an accompanying letter he proudly announced,

Ew. Hochwohlgeboren habe ich die Ehre—Ihre gütige Bewilligung benutzend—hierbei einen vom mildesten Gusstahl massiv geschmiedeten Gewehrlauf zu übersenden.…
Taking advantage of your kind permission, I have the honor to send you a musket barrel forged from the best crucible steel.… At the top of the barrel I have left standing a wedge-shaped piece, which can be cut off cold, and on which any desired test of the tenacity of the material can be made.

He didn’t expect the army to change its small arms policy. Muskets weren’t really what he had in mind. He was seeking a judgment on “the fitness of this material for cannon” (die Tüchtigkeit dieses Materials für Kanonen) and declared that his next step would be to make “an attempt to forge such crucible steel barrels directly as tubes” (einen Versuch… dergleichen Gusstahlläufe gleich als Rohre zu schmieden). Anticipating an enthusiastic response to his first specimen, he was packing two others; they would be on their way shortly.

They went. And they were returned. Linger had his little ways, but he wasn’t that odd. Exasperated, Alfred turned to his favorite foreigners, the British. In his awkward English he informed a Birmingham firm that he was sending “in 1 packet in linnin” two barrels “which it will please you to submit to severe essays and comparisons to gun barrels of iron, especially with regard to the solidity of the material and to the consequence of the greater purity and polish of the soul.”* Should the firm order more than ten thousand pieces—clearly he had reconsidered the value of a musket order; it would be better than nothing—he was prepared to quote a price of ten to twelve shillings per piece. If the order were larger, he would go still lower. But the British, like the Prussians, weren’t interested in steel arms at any price. They were frightfully sorry. They hoped he understood. But there it was.

Also: he would give the home country another chance. Saarn didn’t have the final say in military questions, and after the industrial exhibition he decided to approach Berlin’s General War Department. For the time being his artillery project was shelved; he was definitely concentrating on small arms. Incessant lobbying, and perhaps a few palmed coins, had persuaded Saarn to test one of his barrels. It had performed superbly, even after the metal had been filed to half the regulation thickness and the test charge raised to three ounces of powder. All this Alfred submitted to General Hermann von Boyen, a septuagenarian who had served as Bülow’s chief of staff in the struggle against Napoleon, and who had come out of retirement to become Minister of War. Three weeks after the submission, on March 23, 1844, Krupp had his answer:

In reply to the offer transmitted to me in your communication under date of 1st inst. [Auf das in Ihrem unter dem 1. d. Mts. an mich gerichteten Schreiben enthaltene Anerbieten wird Ihnen eröffnet], you are hereby informed that no use whatever can be made thereof as regards the production of musket barrels, since the present manner of manufacturing these, and the quality of the barrels so produced, at a cost not inconsiderably less, meets all reasonable requirements and leaves hardly anything to be desired.

Even in those days men of war were inarticulate. And after the turgidity had been stripped away, what was left was discouraging. Nevertheless the general did leave the door open to “further deliberation” on “the production of cannon from crucible steel.” Eagerly, Alfred dusted off his artillery plans and proposed that he build an experimental gun. A six-pounder, he believed, would be beyond his present capacity. Eventually he hoped to invest over 10,000 thalers in a complete gun shop (flywheels, new furnaces, a 45-horsepower steam hammer) but there was no point in plunging until Berlin approved the weapon and, he added tactfully, Krupp had orders. He suggested a three-pounder. He could supply one “within a couple of weeks.” The general warmed a bit—he became tepid—and on April 22, 1844, Alfred was given the green light. Unhappily, he had grossly underestimated the time he required; three years later he was still assuring a new minister that the weapon was on its way. It was delivered to the Spandau arsenal outside Berlin in September 1847.

Prussia had received Krupp’s first cannon. And it couldn’t have cared less. Later the political upheavals were blamed for official preoccupation, but they were six months away, and when they did come the critical period was brief. Actually no one was interested in finding out whether or not the gun would fire. There it sat, 237 pounds of Krupp’s best Kruppstahl, lacking even a protective canopy. For almost two years spiders spun webs across the 6.5-centimeter (2.5-inch) muzzle until Alfred, beside himself, finally goaded the sluggish Artillery Test Commission (Artillerie-Prüfungs-kommission) into action. In June 1849 the gun was fired on the Tegel range. Three months later the report reached Essen. Alfred, reading it, was stunned. His weapon shot well, he was told patronizingly; only excessive overloading could destroy it. But “ the need for an improvement of our light guns and our field guns, specifically, hardly exists. All that might be desired is longer life for heavy bronze barrels and greater capacity for those of iron.” Having made an unequivocal point, the commission hedged:

Wir können Sie daher nicht aufmuntern, die Versuche fortzusetzen, wenn Sie nicht im Voraus ersehen, dass es Ihnen gelingen wird, das aus den grossen Kosten entspringende Hindernis für die Einführung derartiger Rohre zu beseitigen.
We are therefore unable to recommend that you continue the experiments unless you can see your way in advance to eliminating the obstacle to the introduction of barrels of this type which arises from their high cost.

_{William Manchester: "The Arms of Krupp, 1587-1968: The Rise and Fall of the Industrial Dynasty that Armed Germany at War", Little, Brown and Company, 2017.}

The early shy assessments in Prussia changed, when they 'tested' these devices in the field against Denmark and Austria between 1864–1866…

In 1856, Fried. Krupp A.G., produced a 9 cm (6-Pfünder-Feldkanone C/61) muzzle-loading rifled gun of cast steel, which gave such good results that Prussia adopted steel for making army guns, which made Prussia the first country to do so.

Krupp guns were purchased by the Russian, Austrian, and the Ottoman Empire armies during the 1860s. By the 1870s, they were being purchased by countries all over the world. Naval guns were also rapidly developed; from 1863, guns were being manufactured for several navies, which included those of Austria-Hungary, the Ottoman Empire and Prussia, among others.

The principal characteristic of Krupp guns is that they are made of steel. Alfred Krupp was introduced to the Bessemer process to mass-produce steel by his London agent and friend, Alfred Longsdon, in 1859-60.2 After a lengthy period of trial and error, this steel was developed to such quality that the royal factory of Woolwich in England acquired steel from Krupp to manufacture guns that conformed to British naval standards. Also, Krupp was one of the first manufacturers to design practical breechloading guns for army use.

Initially, Krupp developed a breechloading system with a wedge breech block, but, because of problems with escape of gas, it continued to manufacture muzzle-loading guns until the adoption of the Broadwell ring allowed the problem to be solved. By this means, they developed the best breechloading guns of the time, assisted by Longsdon's patented designs.3 Initially, Krupp only sold its breechloading guns to Prussia, but, from 1888, it began exporting all over the world. Breech closure was achieved by a steel wedge that slid transversely on a short groove at the rear part of the gun. The movement was imparted by a screw mechanism and the gas-check by the Broadwell ring system.

Krupp also copied the Blakely system to manufacture banded guns. Mayer's Bochumer Verein had the means to produce such a cannon in 1847 as well, but it took them until 1867 to sell one – to the Bavarians.

The cost factor continued to be an issue until 1880 when cast steel and crucible steel procedures were sufficiently optimised from Bessemer, Thomas to Siemens-Martin.

Krupp guns played little part in Germany’s conflict with Denmark in 1864, while their performance in the Seven Weeks War against Austria in 1866 was patchy. There was too much phosphorus in German iron ore for Krupp’s new Bessemer converters to produce good steel from it and there were defects in the design of the company’s breech block, after which Krupp suffered a nervous collapse. Yet enough of the Prussian high command remained faithful to the Kanonenkönig (the Cannon King), the defect in the breeches was cured and he eventually replaced pre-1866 guns with 400 new ones at no charge. When the Franco- Prussian War came in 1870 the French brass muzzle-loaders were no match for them, while Krupp heavy mortars smashed the fortifications at Metz and Sedan.
_{–– Roger Hudson: "Schmiedhammer Fritz. Roger Hudson on a photograph taken in the Krupp works, Essen in 1861, signalling the arrival of a new industrial force in Europe.", History Today, Volume 64, Issue 9, September 2014.}