The history of naval warfare in this world had taken a different course than on Earth.
It was because of mages and abyssal monsters.
A single mage could destroy an enemy surface vessel on his own, and abyssal monsters lurked beneath the waves before surging up to smash enemy ships.
In that environment, the role of conventional fleets had naturally diminished.
Floating platforms for mages. Decoys to draw the attention of enemy abyssal monsters. Cannon fodder on the open sea.
As that reputation soured, mages had gone a step further and imposed technological restrictions on fleet development as well.
And so the Eastern Navy, charged with defending the Empire's seas, was composed of sailing ships armed with nothing more modern than culverin-style cannons.
That was because the East's primary combat force was its Abyssal Monster Corps.
And the defining characteristic of the Abyssal Monster Corps was...
"They're absolutely enormous."
The Tusoteuthis — a colossal giant squid of staggering scale.
Its tentacles alone stretched a hundred meters. The creature had the raw strength to seize a sailing ship and drag it under in a single motion.
No matter how hard the surface vessels fought, there was no way to defeat a massive abyssal monster that hid in the deep and struck without warning.
One sweep of those enormous limbs above the waterline, and several sailing ships would be reduced to splinters in an instant.
For that reason, abyssal monsters could only be countered by other abyssal monsters.
Naturally, the Eastern Navy had come to revolve around acquiring ever-stronger, ever-larger abyssal creatures.
It was the same logic as the big-gun battleship doctrine of my previous life on Earth.
And if you thought about how that doctrine had collapsed, the fall of the Abyssal Monster Corps was, in truth, equally inevitable.
Wield a powerful spear capable of dealing devastating blows, and slowly grind down a massive enemy from beyond its effective range.
For battleships, the carrier had been that kind of opponent. For the great monsters lurking in the deep, submarines would fill that role.
That was why, to dominate the seas going forward, we needed a large number of submarines — a new class of vessel entirely.
The role of destroyers had also become critically important.
To deal with the mid-sized and smaller monsters roaming the surface waters, Depth Charges dropped from destroyers would be absolutely essential.
That said, it wasn't as though battleships had become irrelevant.
In the end, it would be our battleships that finished off the enemy's mages, their naval fleets, and their ports.
"Therefore, in the second half of this year, we will concentrate on the construction of submarines and destroyers."
The budget allocation question was settled.
Three things remained to be worked out.
The armament for the submarines. The submarines' eyes. And the destroyers' anti-submarine measures.
The doctrine of naval warfare in this era centered on clashes between massive monsters. Naturally, the only underwater weapons that existed were rudimentary attack spells — nothing more.
Combat had evolved accordingly, becoming less about large-scale fleet engagements and more about battles between giant creatures.
On top of that, large monsters possessed considerable magical resistance. In an underwater environment where visibility was already limited, the role of mages wasn't particularly significant.
As a result, almost no weapons or spells designed for underwater combat existed.
Weapons development, after all, follows the conditions of the battlefield.
For us, that was an enormous advantage.
Even the most primitive early-WWI-era torpedo boasted an effective range of six to seven kilometers.
The enemy would be torn apart by a barrage of torpedoes before they ever got close to our submarines.
And on top of that, this world had Mana Stones — a natural semiconductor.
Which meant that even without vacuum tube technology, we could approximate guided torpedoes.
The submarines' eyes?
That front was already reasonably well in hand.
During the Albion air raid incident, I had introduced the concept of an early acoustic radar based on the Radar technology we'd used then. Research into that "Radar" had continued ever since.
And we had one advantage that the navies of Earth never possessed.
Large abyssal monsters were virtually impossible to conceal.
The Tusoteuthis — the East's signature abyssal beast — was proof enough of that.
A creature driving itself through the water by churning eight hundred-meter tentacles generates vibrations of truly staggering magnitude.
A seasoned sailor could feel the disturbance within a certain distance without any technology at all.
It was practically advertising its own position.
Against that kind of large underwater monster, even a simple acoustic detector of the sort used on fishing boats would be more than sufficient.
Finally, the destroyers' anti-submarine measure: the Depth Charge.
Submarines would handle the large monsters. With torpedoes and Sonar developed, they could take on smaller ones too — but torpedoes were far too expensive to waste on that.
Besides, submarines couldn't always shadow the fleet. The fleet's anti-submarine defense would have to fall to destroyers, and Depth Charges would be the best tool for the job.
Depth Charges were cheap, simple, and brutally effective.
Pack explosives into a drum, fit a basic water pressure sensor, and roll it off the stern — that's a Depth Charge.
No propulsion system means the weight is almost entirely explosive. The pressure sensor lets it sweep everything clean down to the ocean floor.
There's a reason they were still in use into the twenty-first century.
In that sense, I had a feeling the Design Bureau was going to be very busy for quite some time.
"Lucilla!"
"Yes, Your Grace."
"Forward all of these documents to the Design Bureau as well. That's the list of items that need to be completed within the year."
Once those three weapons systems were finished, we would no longer need to worry about a naval blockade.
Complete naval dominance in the waters around the Belfort Archipelago.
We were close — close to securing the South's right to survive.
***
While the South was busy preparing for the aftermath of the Western annexation, changes were also taking place in the West.
The biggest change, as expected, came from the military side.
For soldiers of the Western territories who had spent their careers with swords, spears, bows, and muskets, the "machine gun" was not merely new — it was alien.
The "machine gun" had no sharp blade attached to it. In an era when even muskets came fitted with bayonets, it was a weapon that felt deeply unfamiliar to the men who saw it.
But no one doubted its effectiveness.
They had watched, with their own eyes, as hundreds of barbarians were cut down without being able to do a thing.
"Joint operation preparations?"
And so the attention of countless soldiers fixed on the notice posted by the Southern Army: "Joint Operation Preparations."
The contents of the notice were straightforward enough.
1. A large-scale barbarian extermination campaign will soon commence under joint Southern and Western Army command.
2. Western Army forces will operate under Southern Army command.
3. Participating soldiers will be issued firearms.
4. As an initial trial, a selection of Western Army soldiers will be chosen to conduct live-fire demonstrations.
Within moments, the area in front of the Southern Army barracks was packed with Western Army volunteers.
Over the past fifty years, a deep well of hatred had accumulated between the West and the barbarian tribes. They had killed each other, raided each other, and driven their relationship to the absolute worst it could be.
If not for practical constraints, they would have been at each other's throats long ago.
For Western Army soldiers who had spent years struggling to hold the barbarians at bay, the appearance of the machine gun was nothing short of a revolution.
Barbarians who wouldn't go down no matter how many times you stabbed or struck them — swept away in an instant?
When the chance to use such a weapon presented itself, no one was going to refuse.
Willie, a soldier of the Western Army, was one of those men.
Lucky enough to be selected as one of the demonstration soldiers, he made his way to the firing range with a heart full of anticipation.
"Willie, soldier of the Western Army, reporting!"
"Good to meet you. I'm the machine gunner who'll be assisting with your demonstration. Here — take these first."
The machine gunner handed him a pair of earplugs.
Willie was briefly puzzled.
'Why would I need earplugs to use a weapon?'
It was a natural thought for someone unfamiliar with firearms. If you wore earplugs during training, you wouldn't be able to hear your superior's orders properly.
That confusion was quickly resolved.
"First lane — fire!"
Brrrrrrrrt—!
The sound of a chainsaw erupted from the machine gun in the distance. Even from over a hundred meters away, the noise drove straight into his ears.
Far sharper and more unsettling than any barbarian war cry. Hearing it, Willie felt something complicated stir inside him.
Fear of an unknown weapon.
And anticipation — the knowledge that he would soon be using it himself.
"Third lane is open, sir."
At his subordinate's report, the machine gunner led Willie to the third firing position.
The machine gun was mounted at exactly shoulder height.
Up close, the "machine gun" was a truly strange weapon.
A solid block of metal — a rectangular body and a pipe riddled with holes. Too heavy to lift, it had to be fixed in place and operated from a stationary position.
And with no knowledge of it whatsoever, Willie had no idea how to even begin using it.
The machine gunner explained it to him patiently.
"This is the stock. You press it against your shoulder to help control the recoil. Rest your hands here, and the moment you pull the trigger, it fires."
Contrary to what he had imagined, pulling the machine gun's trigger required very little force.
The trigger pulled easily enough for a small child to manage.
But the result was anything but light.
Ddddddddd—!
Through the earplugs, the noise hammered into him, and the large wooden target board he had aimed at was simply obliterated.
Willie, and every Western Army soldier who handled a machine gun for the first time that day, all arrived at the same thought.
The South had built a weapon more magical than magic itself.
And perhaps — just perhaps — this barbarian extermination campaign would be different from all the ones before.