3:002 on the 80th day of Winter

My work on the laser cannon reached a fevered pitch in the last few days. I barely ate or slept, trying to finish it before everything fell apart. The boom, boom, boom of the bombardment was sometimes nearer, and sometimes farther, but always present in the back of my mind.

"Command, this is the eastern bastion." said a voice over the radio. "Five sekteth climbing the wall. Over."

"Eastern bastion, this is command. Message received. Out."

He sounded concerned but not panicked. I had the command channel going in the background as motivation. After delivering the radios I had made a few of my own so I could listen in. I had to make and run a pair of wires down from the roof, through a window, and down a hall to get the signal into my workshop. I thought that it would motivate me to work faster. It was less motivating and more terrifying but by then I couldn't turn it off. Every attack, every loss, every bomb dropped, it was overwhelming. I didn't want to fixate on it but I had to listen.

If I could only get the cannon to work right. The test fires where it had worked, if only briefly, had given me hope that we might actually survive. It was like a targeted weapon of mass destruction. In the open field, no number of demons would be able to stand against it. But it didn't work. I had melted through three focusing crystals and five refraction mirrors and it still refused to work. It simply generated too much heat. I had to limit it to ten percent power to get it to work for a mark at a time. Even then it needed ten measures to cool back down before it could be fired again.

The lasers themselves worked fine. They were individually set up to fire a two kilowatt laser with a focal length of roughly fifty meters. They didn't have their own power generation but could store enough fire mana for about thirty marks of continuous fire. That still comes out to about 65 kilojoules of energy, though with light mana involved it doesn't really matter. I then mounted my artificial core to the back and it's power enabled, or at least should enable, continuous fire. The lasers generated very little heat overall because of the efficiency boosting spell I had built into the design. The problem was that the air superheated and that any reflection or refraction of the lasers could not be perfectly efficient. I was currently working on three ways of fixing it. First I had to make the inside of the tube vacuum sealed. Second, I had to circulate water to cool the parts that were overheating. Lastly, I was trying to set up heat sensors I could use to replicate the efficiency spell on the mirrors and lenses I was using.

"Command, this is the eastern bastion." said the radio.

"Three demons killed, two escaped. Seven dead, three injured. Requesting another decade to replace them. Over." Now the guy sounded bored. I couldn't blame him. They had been at this for weeks. Today was even fairly light on deaths.

"Eastern bastion, this is Command, message received from eastern bastion. Two more decades are headed your way from the northern bastion. Out."

I let out a sigh. We were losing. Attrition was only to their benefit at this point. Cinder had an army of roughly eight thousand souls at the start of this but the demons had fielded as many or more in their ranks. And it's not like the average soldier could fight the average demon.

I finished fire magic welding the tube that held all of the mirrors and lenses directing light in the laser cannon. It had a center pipe for a liquid cooling loop I hadn't finished yet. Now I just needed to see if the light chamber would hold a vacuum.

"Okay, let's try this again." I said.

I looked around. Nope, I was alone. I missed Schrodinger. He had been keeping Arin company since her injury. I would try and say hi if I got back at a reasonable hour tonight. Or maybe tomorrow night given the time. First I checked over my weld for microfractures. Clear. Then I used the same trick I had used on the glass bottles to pull a vacuum. Connecting the air magic channel through a copper wire evacuated the air before I simply closed the valve. Lastly, I rechecked everything for leaks. Still clear.

"Command, this is the northern bastion." came a different voice over the radio. "The demons look like they are moving in for another attack. They have a larger force than normal, even a few siege towers. Over."

"Northern bastion, this is command. Message received. We're going to send you another century and put a decade of iron bloods on standby. Out."

Unauthorized use of content: if you find this story on Amazon, report the violation.

I moved on to manufacturing the water cooling loop. The pump had to be just bigger than I could make with my printing spell but small enough that it fit onto the back of the cannon. I also had to make and weld together a ton of small metal fins that would dissipate heat to the air. Then I reconsidered. Wait no. The kind of heat I was generating would quickly boil water. I needed a cooling fluid that could get a lot hotter. Oil? No, that would probably catch fire. Sodium. Ya, that would work. It was solid at room temp so I would need to add heaters that could get it up to temperature but then it would be able to transfer an enormous amount of heat to the heat sink. Of course that meant I needed to coat the inside of the cooling loop with a ceramic layer that would keep the pipes from corroding.

"Command, this is the northern bastion again. Their siege towers are better shielded than last time it looks like they will make it to the walls. How long until the reinforcements arrive? Over."

"Northern bastion, this is command. They are marching now. They should be there in ten measures. Out."

I was impressed that the defenders had adapted to radios so quickly. It was rough in the first few days but now it was like they had always had them.

"Command, this is the northern bastion, the siege towers had a water magic enchantment to boost their speed. Three have made contact and are pouring out demons now. Over.'' He sounded worried now.

"Northern bastion, this is command. We are sending the mages as well. Hang on. Out."

Then the northern bastion guy started cursing.

"They have a killalith, no scratch that they have three killaliths." he said, losing all radio discipline.

A killalith was a kind of demon I had only seen once before. They were large masses of black oily tentacles with sharp blades or spear tips caping each one. They were mostly aquatic but could swim through the air for short times using water magic. To cap it all off they had three beaks that were sharp and strong enough to bite through the legion plate with ease. I scrapped the sodium metal cooling loop for version two and settled on oil for this design. I needed to finish it now.

"North bastion, this is command, what is happening? Over.''

There was only silence.

"Northeast or Northwest bastions, this is command. What is happening on the northern bastion? Over."

"This is the Northeast bastion, I can see the siege towers from here but that's about it. I can tell that there is fighting on the walls but can't tell how it's going. Over."

"Northeastern bastion, this is command. Message received. Out."

Things devolved from there to trying to find other groups that could be sent to the fight. Trying to force it, I ended up breaking off a blade in the radial pump assembly. Cursing, I focused on remaking the part. My mind felt sluggish and my magic weak. I hadn't rested enough and would soon deplete my mana. Rushing to put the pump in place I then moved to the other side of the workshop where the mineral oil was stored. I had to make a funnel that was the right size for the opening and I was kicking myself for not thinking ahead when more news came in.

"Command, this is the commander of the forty-first century. There is heavy fighting on the wall at the northern bastion. With the siege towers in place the demons are scaling the wall in force. We will try to hold them back but we won't be able to do much if the mages can't take out those towers. Over."

"This is command, the iron blood mages en route will prioritize the towers. Your orders are to hold the line and protect the civilians. Out."

With the vacuum and the cooling loop finished the last thing to do was to connect the temperature sensors in the tube to a core that would suppress the rise in temperature by ending all worlds where it got hot too quickly. I had to run wires from dozens of high temperature thermocouples to a set of electronics that would measure how quickly their temperature was changing. A wave of doubt ran through me. This was such a cobbled together mess. It would never work. It would blow up in my hands.

"Command, this is the commander of the forty-first century. The iron blood mages took down two of the towers but were killed before they could destroy the third. There are too many, our position will be overrun soon. Send reinforcements. Over."

"Commander of the forty-first century, this is command, we are sending centuries from both north-eastern and north-western bastions. Hold out as long as you can. Out."

It didn't matter. The laser cannon had to work. I tied off the last few wires. Turned on the pump and activated the switch that primed all three hundred lasers. All told, this cannon would reach almost a megawatt of power. I checked the temperature sensors. All functional and holding steady. I shifted the weapon to pick it up. It was at least forty kilograms, including the heavy artificial core at the back along with the heatsink.

I hefted it and pointed it at the target I had set up at the other end of the room. It hung below my forearm and was designed to shoot from the hip. I pulled the trigger on the handle and heard a loud CRACK. Letting go of the trigger, I checked the oil temperature. It had jumped from twenty degrees Celsius to eighty degrees in that short blast. The solid steel target was completely destroyed with a deep glowing line cut across the back wall.

"This is the commander of the forty-first century." Now he sounded out of breath and scared. "Our formation has collapsed. Demons are flowing past us into the northern district of the city. We can't hold on. I am ordering a fighting retreat and moving to group up with the ninth century. Over."

My heart sank. Aegis manor was in the northern district. I tied off a strap to the front and back of the laser cannon and slung it over my shoulder. I made sure my armor was in place and put on my helmet. I needed to move now. I ran downstairs and out the main doors of central command. I jogged as quickly as I could north. I prayed to Mez that I would make it in time.