[High-Tech] Understanding the practical rate of fire for a cannon.

[Michael Thayne]

I'm trying to get a better grip on how to interpret GURPS stats for crew-served weapons, particularly how to translate statistics like RoF and Shots into a practical rate of fire. Specifically:

• If you have a cannon with something like Shots 1(4) crewed by a gunner and a loader, can the gunner take Aim maneuvers while the loader is taking a series of Ready maneuvers to load the weapon? Or does the gunner have to wait until the loader is done loading before the gunner can start taking aiming?
• What does the fractional RoF for the Motovilikha D-81TM (the big Russian tank gun) in High-Tech mean? Does it mean it takes eight maneuvers for the gunner to fire? Or just that the gunner has to wait 7 seconds between attacks for the autoloader to reload the gun? In the latter case, can the gunner take Aim maneuvers while the autoloader is doing its thing?

[AlexanderHowl]

No, loaders have to get in the way of the gunner and move the cannon to facilitate loading.

[Michael Thayne]

Originally Posted by AlexanderHowl

No, loaders have to get in the way of the gunner and move the cannon to facilitate loading.

This seems right for muzzle loaders, but would it be true of a breech loader? I particularly wonder if it would apply when you're talking about, say, a WWII-era tank.

[Fred Brackin]

Originally Posted by Michael Thayne

This seems right for muzzle loaders, but would it be true of a breech loader? I particularly wonder if it would apply when you're talking about, say, a WWII-era tank.

Look at the weights involved. The shells for the guns for the Panzer IV and the Sherman weight 23 and 24 lbs. So first that weight slams into the gun and then the breech (which should be a significant percentage of the gun's 1000 lb+ weight) thuds home. These motions probably did make the gun move in response and should have made a coaxial sight move too.

You wouldn't be able to start aiming on the turn after the gun fired because the tank rocks on its' treads from the recoil. For that matter, anyone who could concentrate through the noise of firing ought to have Unfazeable at least.

[Anthony]

For guns listed in High-Tech, I would say you aren't going to do what GURPS calls an aim maneuver, though you could certainly spend the reload time updating your firing solutions so you know the bearing and elevation you want for your next short.

[Michael Thayne]

Originally Posted by Fred Brackin

Look at the weights involved. The shells for the guns for the Panzer IV and the Sherman weight 23 and 24 lbs. So first that weight slams into the gun and then the breech (which should be a significant percentage of the gun's 1000 lb+ weight) thuds home. These motions probably did make the gun move in response and should have made a coaxial sight move too.

Does the same logic apply for more recent designs with autoloaders? (After posting the OP I noticed the autoloader rules are somewhat clarified in the High-Tech errata, but it's still unclear if you can Aim while the autoloader is running.

[Fred Brackin]

Originally Posted by Michael Thayne

Does the same logic apply for more recent designs with autoloaders? (After posting the OP I noticed the autoloader rules are somewhat clarified in the High-Tech errata, but it's still unclear if you can Aim while the autoloader is running.

Modern tanks rock on their tracks probably even more than WWII models and only the T-72 family uses an autoloader. It may stay that way too as the T-72 autoloader makes the inside of the turret into a deathtrap if it gets penetrated. The gunner and commander are surrounded by over a thousand lbs of naked nitrocellulose.

You might see common autoloaders in the future if you get totally unmanned turrets. separated from the hull by a firewall. Aiming would be electronic then of course but the tank still obeys Newton's 3rd law.

[Ulzgoroth]

Originally Posted by AlexanderHowl

No, loaders have to get in the way of the gunner and move the cannon to facilitate loading.

That's certainly not going to be true in all cases. You could easily* lay out a cannon such that the loader can work without getting in the gunner's space or moving the gun.

* May be less easy in cramped environments or when the ammunition is very heavy.

My impression is that the usual practice of modern US tank gunnery doesn't has the gunner stay on their scope during the reloading, but I could be wrong about that.

There are definitely cannons where the loader can feed more ammunition while the gunner is shooting - but those are of course automatic cannons where the loader is adding ammunition to an automatic feeder rather than directly loading the breach.

In a turret, there should be little problem with doing horizontal traversal while reloading, since the loader will be inside the traversing body. Elevation adjustment could be a problem, since you're normally moving the gun relative to the turret when you do that. OTOH the adjustments there are usually small.

Addendum: Automatic loading assists often require the gun go to a particular elevation to work. That would probably interfere with aiming, unless the gunner's sight somehow disengages from the gun and then re-aligns. Which seems like it probably wouldn't be accurate.

[Rupert]

Originally Posted by Ulzgoroth

Addendum: Automatic loading assists often require the gun go to a particular elevation to work. That would probably interfere with aiming, unless the gunner's sight somehow disengages from the gun and then re-aligns. Which seems like it probably wouldn't be accurate.

Actually, that's very often how they work. Rather than trying to fully stabilise the whole weight of the gun, only the sights are fully stabilised and they are not mechanically linked to the gun. When you want to fire either the gun is synced to the sights or the system fires the gun at is senses it passing through the correct line.

Aside from anything else, for manually loaded guns if they were stabilised when being loaded the loader would get smashed by them if the tank went over a bump. So they get stabilised in that they don't bounce all over, but they aren't locked onto a target all the time.

At the most massive end, big naval guns in the 20th century had next to no connection to their sights, which were often in a completely different part of the ship (though the turrets often had backup sights), and the sight and rangefinder operators most certainly kept doing their thing while the guns were being reloaded, as did the fire control computer operators, etc. That said, with these guns while the turrets would be constantly trained, the guns' elevation was adjusted after loading, even if they were loaded without being moved to a fixed elevation - they were just too heavy for it to be safe having them moving while their crews were serving them.

[Ulzgoroth]

Originally Posted by Rupert

Actually, that's very often how they work. Rather than trying to fully stabilise the whole weight of the gun, only the sights are fully stabilised and they are not mechanically linked to the gun. When you want to fire either the gun is synced to the sights or the system fires the gun at is senses it passing through the correct line.

Huh. That certainly solves problems, but I am surprised it's precise enough to be considered satisfactory.

Originally Posted by Rupert

At the most massive end, big naval guns in the 20th century had next to no connection to their sights, which were often in a completely different part of the ship (though the turrets often had backup sights), and the sight and rangefinder operators most certainly kept doing their thing while the guns were being reloaded, as did the fire control computer operators, etc. That said, with these guns while the turrets would be constantly trained, the guns' elevation was adjusted after loading, even if they were loaded without being moved to a fixed elevation - they were just too heavy for it to be safe having them moving while their crews were serving them.

Sure, but big naval guns accept quite a lot of scatter.