When you first start Iron Nest: Heavy Turret Simulator, you're standing in a small office annex of the walking artillery unit you call home. A board in front of you lays out the process of firing the turret's cannon. First you measure the distance and bearing to the target, calculate the necessary turret elevation, load the gun, angle and rotate the cannon, and then fire the shell. It all looks simple enough.

However, seeing as the inside of the Iron Nest is the size of a small warehouse, this artillery unit surely dwarfs the 'Gustav', the train-mounted cannon Germany built to blast the French forts of the Maginot Line. And, seeing as this machine looks to be of a similar vintage, getting that gun to fire is going to be a muscularly manual process.

On the office desk is a vinyl. I drop it onto the record player, crank up the volume, and head to the map table, pencil and compass in hand, military marching loudly blaring out of the Iron Nest's tannoy.

Iron Nest, a game inspired by the still-in-development, PVKK: Planetenverteidigungskanonenkommandant, revels in tactility. Similar to games like Jalopy and My Summer Car, this is a simulation that finds its fun not in the result of the action, but the process of making it happen. At the beginning of a mission in Iron Nest a giant teletype fixed to the wall of the turret rattles out your objectives and relevant details with the chatter of a rapidly moving typing arm.

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High Command to Iron Nest:
Begin calibration firing test.
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- Plot you firing trajectory to Target on the map.
- Fire HE shell at the target.
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IRON NEST location - H3 5:5
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TARGET COORDINATES:
Target#1 is at- Q4 4:2
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Glory to Castille! ! !

Over at the map table, which is a vast 12 footer, the likes of which I've only seen in World War II movies, there is a little wooden model of the Iron Nest. Off to the left of the map, laid out in orderly lines, are icons of different colours and shapes. I pick up a fetching little red number and place it at grid square Q4 4:2. I then draw a line from the target to my turret and the distance and bearing of the line are automatically added to the little clipboard I carry with me.

I copy the distance into a nearby targeting computer and it lights up on a panel showing how many powder charges are needed to launch the shell all that way. Twist the dial to the indicated light, hit the calculate button, and out pops a little card stating the necessary turret elevation. From there, it's over to the loading cylinder and firing tube.

The Iron Nest fires massive shells, they're six foot at least. By pulling levers and dragging mechanical arms, you can spin through the turret's magazine and select the correct shell type and slide it into the firing tube. Pulling yet more levers you load in the powder charges, and with a final heave you load everything into the cannon and lock the chamber.

The process continues, as you raise and rotate the turret to match all the notes on your clipboard. It's a very satisfying, functionary job. Dials are spun, switches are flicked, levers are pulled, list items are checked off. When I finally have everything lined up and ready, I flick the final confirmation switches, yank down on a firing chain and the entire room shakes with the launch and roar of the blast.

It's as I watch a mechanical arm track the shell's trajectory on the map and see it travel in a wildly different direction from my target, shooting off the map entirely, that I realise I should have drawn the pencil line from the turret to the target, and not the other way around. I sure hope it's landed in an abandoned field somewhere…

I go back to map, redraw the line, and chase that correction through the rest of the process before firing the cannon again. This time, the shell is a direct hit. The teletype chatters out another message.

High Command to Iron Nest:
Calibration confirmed. Iron Nest is combat Ready.
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Stand down and await operational orders.
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Retire to your bed and get rested. Victory depends on your readiness at any time.
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Glory to Castile! ! !

The newspaper report that greets me after I lay down in my bunk gives me some misgivings. But, why should I doubt the press…

Over the next few missions, misgivings become outright suspicions. My part in Castile's campaign against the anti-monarchists comes to a head when we recapture the royal city. My orders are to shell the infantry holding the city, calculating firing locations by combining the reports from different spotter units. Using the spotters position and the bearings they provide, I draw lines across the map looking for the points where they interact. That's where I aim my shells.

In the heat of the moment, I admit I'm carried away with the tactile fun of pencilling out lines on the big map table, pulling on levers to ram the shell and powder charges into the turret, twisting all the confirmation switches to green, and yanking down on the handle to fire the gun. The jumps and vibrations of the igniting powder's explosive blast sends the service lights that hang from the ceiling swinging, and back at the map table I watch the tracking arm confirm I was spot on in my trajectory calculations. A stopwatch in the bottom right of the screen counts down the seconds to target. It's a thrilling moment.

And then the shell lands.

Black and white aerial photographs bloom over the impact point, transforming the pencil markings of my intended action into a record of what I did. Red markers show the enemy buildings and battalions that I've erased from existence. But mixed in with the red wooden icons, are the blues of allied units and civilians. Back at the teletype, frantic messages come through telling me to cease fire. I hit the anti-monarchists, but I also wiped out a loyal police unit in the sector. The mission isn't over, though, I've four more targets to hit, all of them in the city.

By the end of the mission, I am thoroughly conflicted. Even if it's not a surprising revelation, I still find the knowledge of the impact leaves me deeply uncomfortable. I don't know if Iron Nest's developers will be able to sustain that discomfort over a campaign – nor if following the firing process over and over will continue to thrill - but it's a welcome complexity in a game that, on first flush, looks to be big silly fun,

Perhaps my mistake was not playing the marching music again.