On October 12, after breakfast, the was tested.

The location was Tatsumi Bay.

Since it was far enough away from the aquaculture tanks, all the visitors ......<> and the <> family were taken aboard the cruiser <> to observe the test.

"How does an <> work, anyway?"

Reinhardt asked, intrigued before the test.

"Reinhardt had a short wand that was implanted with magic and activated only by pouring mana into it, didn't he?"

"That's the one I miss ......."

Four hundred years ago,...... Jin and Reinhardt had just met. Reinhardt was a diplomat of the Shoro Kingdom and was visiting the Kingdom of Elias with Erza.

When fighting off the Death Serpent that attacked the port of Potlock, they had attacked it with a wand containing a Flame Lance.

"The idea is the same as that. "The idea is the same as that, except that mana is supplied by magi stones, and there is a device that speeds up the activation of the magic.

Reinhardt sniped at Jin who said casually.

"No, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no.

<, a time lag of one or two seconds would not be of much concern.

But as a torpedo, .......

"Is it called a tip ......?　It must be triggered within zero-tenths of a second ...... or zero-tenths of a second?"

As expected of Reinhardt, he had accurately detected the conditions for triggering the phenomenon.

"Oh, as expected. Yes, that's right. That's why I devised this torpedo's fuse."

What kind?

"It's stopped just before it goes off. To activate it, you need to ...... well, in terms of chanting, you just need to add one word ...... or half a word and it's done."

"No, no, that's not so easy!

In such a state, Reinhardt said, the mana would just be dripping down the drain.

"That's right. That's why I devised it."

"How?"

"Just before you fire, you activate the fuse."

The idea is like a hand grenade, but by activating the fuse when you use it, you shorten the time it takes to fire.

There is no need to worry about the grenade exploding if too much time elapses.

In short, the fuse is activated when the launch button is pressed, and the engineering magic is constructed during the time it takes for the torpedo to land. The torpedo should be in a state halfway before it is triggered.

Then, at the moment the torpedo hits the opponent, the engineering magic is triggered by the last push of the button.

This way, you can deploy engineering magic on the opponent's surface with no time lag.

In this case, the main engineering magic was <.

"The moment the tip of the torpedo makes contact, Forming is activated and a hole is made in the armor. Through that hole, the second half of the torpedo penetrates inside, causing minor destruction."

"I see."

"I see." "It would be impossible with something like a supersonic rocket, but with a torpedo's speed, it should be okay."

"I see."

"So, we're going to conduct an experiment."

We had already conducted several tests in the prototype stage, so now it was time for the actual firing.

A 1 meter square adamantite plate, 10 centimeters thick, was placed in a shallow area about 1 meter below the sea surface. It is a very heavily armored plate weighing as much as 2 tons.

It is fixed between two steel pillars erected on the seafloor.

The location is just in view of the cruiser.

"Are we ready?"

<

<

<

"Okay, Killer Whale, let's go!"

The new Orca can be remotely controlled with high precision. Of course, you are in control.

The target is one meter below the surface of the sea, so he can see it clearly from the ship.

< were staring at the sea with bated breath.

"Oh, here comes the killer whale!"

He arrives within a minute of being dispatched. < and moves away from the target.

"Kuhu, I guess is a very special outfit, isn't it?"

Saki said.

"They are quite different from other submarines, aren't they?

Hannah also chimes in.

Well, some of the submarines look like flat triangular rays, some are hemispherical, and some are submarines that look like submarines.

"Yes, yes. ...... Jin, why is the shape of the submarine you showed me before so different from that of the submarine at Jin's place, the <?"

Marcia, being Marcia, took the opportunity to ask Jin about the shape of the submarine.

"What?　...... uh, oh, I see."

Jin explained, of course, what he knew about Earth's submarines, which were sometimes cigar-shaped, sometimes teardrop-shaped, and sometimes tear-drop-shaped.

It could be cigar-shaped or teardrop-shaped.

"The submarines in my world are very limited in terms of construction methods and materials."

What do you mean?

I'll explain it to you now. ...... First of all, you understand that water pressure is a very powerful force, don't you?"

Of course. It increases by one atmospheric pressure at about 10 meters, right?

"Yes. In that sense, it's easier to keep a spacecraft airtight.

In the case of a spacecraft, the pressure inside is one atmosphere, and if there is a vacuum outside, the pressure is zero, and the difference is only one atmosphere (excluding spacecraft that are designed to land on a planet with a high pressure).

In a submarine, on the other hand, the pressure difference between the outside and the inside is already 1 atmospheric pressure after diving 10 meters, The pressure difference between the inside and the outside of a submarine is 1 atmosphere after a dive of 10 meters.

The pressure inside a soccer ball is 0.6 to 1.1 atmospheres.

In the case of a car tire, the unit used is different, but when converted to atmospheric pressure, it is within the range of 2 to 3 atmospheric pressure (in the case of a passenger car; in the case of a large truck, it is more than 8 atmospheric pressure). (In the case of passenger cars, many large trucks have tires with a pressure of 8 bar or more).

"Since they cannot be molded in one piece, seams are formed, which inevitably weaken the parts."

"Oh, we talked about that a while ago, didn't we?"

"Yes. So, in terms of materials, it is also difficult to make large windows out of transparent materials. I mean, it doesn't make much sense.

After explaining what he meant, Jin continued.

"First of all, it is dark underwater.

Even in clear water, the amount of light is reduced to 1/100 after diving 100 meters. Even in murky water, it quickly becomes completely dark.

In such a dark place, visual observation is not very effective.

And if the submarine is to be used as a weapon, turning on the lights is also undesirable. It is like telling the enemy your position.

"That's why it's normal to use sonar to find out each other's position underwater."

"I see. But in the case of djinn, there is no such need, and the design is different because of the strong, transparent material.

"That's one thing, but don't panic.

Jin continued to explain.

"Also, usually you need air, or rather oxygen.

"Yes, because of the crew.

"That's not all. Submarines in my world were also powered by internal combustion engines.

The diesel engine generates electricity, which is then used to power the motor.

To do this, an air intake tube called a snorkel must be protruded into the sea.

When the submarine dives deep, the diesel engine is turned off and the electricity stored in the battery is used, but not for very long.

A nuclear submarine would be able to overcome this problem because it would not need oxygen to generate electricity.

"I see. In Jin's case, he's able to regenerate air with his magical tools."

"That's what I mean. Also, submarines were originally developed to attack ordinary ships. So they would use a to observe the ocean."

In this case, the part protruding from the surface of the sea should be as small as possible, so there is a part called a <>, which is equivalent to a <> in a ship.

"This also acts as water resistance."

"Oh, so in the case of a djinn, there's no need for a periscope, so there's no mast."

"That's what I meant. Well, even if we did, we would only use a periscope.

While they are talking like this, the killer whale has completed a distance of about 500 meters from its target.

Finally, the experiment is about to begin.