Tank vs. Cannon

[Rupert]

Originally Posted by Anthony

22mm of WWII armor steel should be around DR 60 (penetration is normalized for RHA being DR 70/inch, and I would expect early tanks to be comparable to RHA).

Not sure about the penetration of the 12 lb gun, though. You can essentially view it as a 144 weight (5.24*scale) 12 gauge shotgun (12 gauge means a spherical lead ball would be 1/12 lb, 12 lb means a spherical lead ball would be 12 lb), and 12 gauge slugs are generally stopped by level IIIa armor (DR 12), so I'd be tempted to assign a (0.5) armor divisor.

I'd be concerned about spalling, rivets, and from the shock of impact. Getting hit by a 12 pound ball of iron moving at high sub-sonic speeds is going to make quite a bang. The armour plates might also simply get bent and deformed to the point where they fall off.

On the other hand, if the ball hits at an oblique angle, it's probably just going to bounce off and do nothing other than make a loud clang!

[Sam Cade]

One thing to consider is that everyone in the vicinity is going to know *exactly* where the cannon is emplaced as the huge plume of white smoke billows forth.
The crew better shoot then scoot with haste.

[copeab]

Originally Posted by Sam Cade

One thing to consider is that everyone in the vicinity is going to know *exactly* where the cannon is emplaced as the huge plume of white smoke billows forth.
The crew better shoot then scoot with haste.

It sounds like the tank is not supported by infantry, so the overworked TC is unlikely to notice anything after his tank rings like a gong.

[Rupert]

Originally Posted by Sam Cade

One thing to consider is that everyone in the vicinity is going to know *exactly* where the cannon is emplaced as the huge plume of white smoke billows forth.
The crew better shoot then scoot with haste.

Another thing to consider it that guns were usually used in pairs or units of four, so if they are set up down a side street in ambush at short range, the tank could well get hit by 2-3 balls from the side, which would be pretty exciting for the crew. I would expect a ball that hits the tracks or track skirts to be stopped by them, but to jam the track in the process. A ball that hits those thin vertical plates is probably going to go through, and if not smash the plate. Either way most crews would be out of the tank quick-smart.

[smurf]

Would the Merrimack vs Monitor battle be any help?

Most Cannon at that time were firing 1200fps/366mps. Shot was a ball and not a ballistic round designed to travel at supersonic speeds.

[johndallman]

Originally Posted by smurf

Would the Merrimack vs Monitor battle be any help?

Not really. Their armour was backed by substantial thickness of timber IIRC, which limits the kind of damage to armour that we're expecting on a light tank.

[ericthered]

Originally Posted by johndallman

Not really. Their armour was backed by substantial thickness of timber IIRC, which limits the kind of damage to armour that we're expecting on a light tank.

Also, it was fought with exploding shells rather than solid shot. Solid cannon balls will take hours to sink a ship. exploding shells will take a ship apart in short order.

I'd trust the raw numbers the weapons and armor give in gurps. I don't know what the penetration of the armor will look like, but if gurps says that a 12 lb ball at 450 m/s goes through 18 mm of steel plate, I'm inclined to believe it, especially with a basic iron plate and a solid steel ball.

[Rupert]

The tank in question (the I-Go) had actual armour plate, though very thin.