“The gas seal would be complete. But it would be the devil’s own job — and a slow one at that — to screw a long bolt in and out between each shot.”

“Of course. So let me show you…”

Parrott went to the rear of the gun and reached up to strain at a long lever. He could barely reach it, nor was he able to pull it down. The taller Swede who, despite his advanced age, was immensely strong, reached past the small gunsmith and pulled the bar down with a mighty heave. The breech-block rotated — then swung aside on a large pinned hinge. Ericsson ran his fingers over the threads on block and barrel.

“It is an interrupted screw,” Parrott said proudly. “The theory is a simple one — but getting the machining right was very difficult. As you can see, after the breach and the breechblock have been threaded, channels are cut in each of them. The block then slides forward into place. And with a twist it locks. A perfect gas seal has been accomplished by the threading. After firing the process is reversed.”

“You are indeed a genius,” Ericsson said, running his fingers over the thick iron screw threads. Possibly the only time in his life that he had praised another man.

“If you will show me the ship on which it will be mounted…”

“Difficult to do,” Ericsson said, smiling as he tapped his head. “Most of it is inside here. But I can show you the drawings I have made. If you will step inside my office.”

Ericsson had not stinted himself with the government’s money when he had designed a workplace for himself. He had labored for too many years in the past in drafty drawing rooms, sometimes only feebly lit by sooty lanterns. Now large windows — as well as a skylight — illuminated his handsome mahogany-framed drafting table. Shelves beside it contained models of the various ships he had designed, other inventions as well. The drawing of Virginia was spread across the table. He tapped it proudly with his finger.

“There will be a turret here on the forelock, another aft. Each will mount two of your guns.”

Parrott listened intently as the Swedish engineer proudly pointed out the details that would be incorporated into his latest design. But his eyes kept wandering to a chunky metal device that stood on the floor. It had pipes sticking out from it and what appeared to be a rotating shaft projecting from one side. At last he could control his curiosity no longer. He tried to interrupt, but Ericsson was in full spate.

“These turrets will be far smaller than those I have built before because there will be no need to pull the gun back into the turret after firing to reload through the muzzle. Being smaller the turret will be lighter, and that much easier to rotate. And without the need of pulling the guns in and out after each shot the rate of fire will be faster.”

He laughed as he clapped the small man on the back, sent him staggering. “There will be two turrets, four guns. And I shall design the fastest armored ship in the world to carry these guns into battle. No ship now afloat will stand against her!”

He stepped back, smiling down at his design, and Parrott finally had a chance to speak. “Excellent, excellent indeed. When I return I shall begin work on the other three guns at once. But pardon me, if you don’t mind — could you tell me what this machine is?”

He tapped the black metal surface of the machine and Ericsson turned his way.

“That is a prototype, still under development.” He pointed back at the drawings of his iron ship. “This new ship will be big — and with size comes problems. Here look at this.”

He picked up a half-model of Monitor and pointed out the steam boiler. “A single source of steam here, that is more than enough in a ship this size. The turret you will notice is almost directly above the boiler. So it was simple enough to run a steam line to it to power the small steam engine that rotates the turret. But here, look at the drawing of Virginia. Her engine is on the lowest deck. While the turrets are far above, fore and aft. This means that I will need insulated steam lines going right through the ship. Even when they are insulated they get very hot. And there is the danger of ruptures, natural or caused by enemy fire. Live steam is not a nice thing to be near. Should I have a separate boiler under each turret? Not very practical. I have considered this matter deeply, and in the end I have decided to do it this way.”

“You have considered electric motors?”

“I have. But none are large enough to move my turrets. And the generators are large, clumsy and inefficient. So I am considering a mechanical answer.” He looked over at the engineer. “You have heard of the Carnot cycle?”

“Of course. It is the application of the second law of thermodynamics.”

“It is indeed. The ideal cycle of four reversible changes in the physical condition of a substance. A steam engine works in a Carnot cycle, though since the source of energy is external it is not a perfect cycle. In my Carnot engine I am attempting to combine the complete cycle in a single unit. I first used coal dust as a fuel, fed into the cylinder fast enough so that isothermal expansion would take place when it burned.”

“And the results?” Parrott asked enthusiastically.

“Alas, dubious at best. It was hard to keep the cylinder temperature high enough to assure combustion. Then there is the nature of the fuel itself. Unless it is ground exceedingly fine, a weary and expensive process at best, it tended to lump and clog the feed tube. To get around that problem I am now working with coal oil and other combustible liquids with improved results.”

“How wonderful! You will have a self-contained engine under each turret then. You will keep me informed of your progress?”

“Of course.”

Parrott thought of the patent of the land battery that had been hanging on his office wall for many years. A most practical idea. Lacking only an engine sufficiently small to move it.

Was Ericsson’s machine going to fulfill that role?

Gustavus Fox was signing papers at his desk when the two Irish officers came in. He waved them to the waiting chairs, then finished his task and put his pen aside.

“General Meagher — do I have your permission to ask Lieutenant Riley a few questions?”

“Ask away, your honor.”

“Thank you. Lieutenant, I noticed that scar on your right cheek.”

“Sir?” Riley looked concerned, started to touch the scar, then dropped his hand.

“Could that scar once have been — the letter ‘D’?”

Riley’s fair skin turned bright red and he stammered an answer. “It was, sir, but…”

“You were a San Patricio?”

Riley nodded slowly, slumped miserably in his chair.

“Mr. Fox,” Meagher said. “Could you tell me just what this is all about?”

“I will. It happened some years ago when this country went to war against Mexico. Forty years ago. There were Irish soldiers in the American army even then. Good, loyal soldiers. Except for those who deserted and joined the Mexican army to fight for the Mexican cause.”

“You never!” Meagher cried out, fists clenched as he rose to his feet.

“I didn’t, General, please. Let me explain…”

“You will — and fast, boyo!”

“It was the Company of Saint Patrick, the San Patricios they called us in Spanish. Most of the company were deserters from the American army. But I wasn’t, sir! I had just come from Ireland and I was in Texas on a mule train. I was never in the American army. I joined the Mexicans for the money and everything. Then when we were captured General Winfield Scott wanted to hang the lot of us. Some were hung, others got off with being lashed and branded with the ‘D’ for deserter. I swore I had never been in the army, and they could find no record of me whatsoever. They believed me then so I didn’t get the fifty lashes. But they said I still fought against this country so I was branded and let go. I rubbed the brand, broke the scab and all, so you couldn’t see the letter.” Riley raised his head and straightened in his chair.