Hypothetical time.

This almost happened in an encounter I am running right now. Two mobs of 10 Ork Boyz led by a Loota Get Ready for Da WAAAAGHHH and rush a Chimera. Now the Chimera was able to get out of the way of the charge in time, but let's say it didn't.

Let's say the Orks swarm it, climb on it, surround it and get on top of it. Now, as the GM I want the Orks to try and rip the top hatch off of the vehicle. How do I go about doing that?

I realize it would be the Ork strength test (perhaps modified by the unit strength) vs. what? What hypothetical strength score would the hatch of a Chimera have? It would be easy to figure out if it was an open hatch and the squad inside the vehicle was trying to hold it shut.

Opposed strength tests.

But what if it is simply locked? Can it be done? I like to think that anything can be accomplished given the proper amount of violence. What do you guys think?

Personal house rule that I apply that might serve you well here.

When players are in a vehicle they must declare the action of locking it. If they lock it, they lose the ability to bail out if it is destroyed.

Becomes a question then of what's more important to your players; Escape or preventing boarding action?

As for Strength score...one of the Chimera's armour facing? Probably rear or side.

Well a Chimera, if I recall, has three entrances. One which doubles as the driver's view port, another on the turret while the last is at the rear where the troops move. Since you specify top, I assume that's the commander's hatch.

Now, in this case, I'd rate it as being a -10 strength test, unless someone is there holding it down or making sure no one opens it. In this case, I'd likely make it an opposed strength test, with the crewmen getting a +20 or +30 bonus.

As the turret's roof armor isn't nearly as strong as its side or front, another possibility is to allow the orkz to carve their way in. In this case, I'd give my players a few turns time limit before they manage to break inside.

In either case, the vehicle can shake off the orkz, most probably using Evasive Manoeuvring, with the penalty to BS to hit it translated as a penalty to either strength or agility for the orkz to hang onto the frantically moving vehicle.

Mhmm. We're talking about a locked metal hatch - personally I'd make the Strength test considerably more difficult than that. Characteristics and Skill Tests have difficulties designed towards normal human people (the fact that the attacker is an Ork is represented by their higher Strength), and how likely is it that some human could just rip a locked metal door open?

The Ork should have a chance, but it should be fairly low (-30 = "Very Hard"). If the Ork doesn't succeed on their first turn, however, perhaps his boyz will try to help, in combination with material stress lowering the difficulty to -20 on the 2nd turn, and one more time to -10 on the 3rd turn. If the crewmembers notice what's going on and have at least one person pulling the hatch down from below, I'd simply assign an additional -X modifier to the Orks' tests (where X is the human characters' combined Strengh Bonus x2, with the caveat that no more than 3 of them can pull on the hatch at the same time) rather than making it opposed.

If you go for opposed, I would recommend to at least consider adding bonuses for Assists, though.

First question here is: should opening the closed hatch be easier or harder than breaching the hull?

I think it should be equally hard because otherwise Chimera would have huge weak spots where the doors are. That should be reflected in rules, which isn't.

And if there is no way to grab the door from the outside, lever it or pull there is no natural way to rip them off.

There isn't any amount of violence that would open those door before breaching it first.

Is there not an external hatch? I assume there would have to be, otherwise how would Imperial personnel access an empty vehicle aside from leaving the hatches open at all times?

Mhmm. We're talking about a locked metal hatch - personally I'd make the Strength test considerably more difficult than that. Characteristics and Skill Tests have difficulties designed towards normal human people (the fact that the attacker is an Ork is represented by their higher Strength), and how likely is it that some human could just rip a locked metal door open?

The Ork should have a chance, but it should be fairly low (-30 = "Very Hard"). If the Ork doesn't succeed on their first turn, however, perhaps his boyz will try to help, in combination with material stress lowering the difficulty to -20 on the 2nd turn, and one more time to -10 on the 3rd turn. If the crewmembers notice what's going on and have at least one person pulling the hatch down from below, I'd simply assign an additional -X modifier to the Orks' tests (where X is the human characters' combined Strengh Bonus x2, with the caveat that no more than 3 of them can pull on the hatch at the same time) rather than making it opposed.

If you go for opposed, I would recommend to at least consider adding bonuses for Assists, though.

Eh ... Material stress would take a (long) while to build up to any meaningful amount on the hatch's mechanisms or the frame it is set in - there's not going to be a lot of give in it, which is where materials stress can most rapidly be generated. Even before you get into it being 40k and overengineered and overbuilt by default.

To be honest, I think that the Orks would be far more likely to wind up ripping off what they used for handholds long before they ripped the hatch open (assuming it's locked). This may or may not have a side effect of jamming whichever hatch they tried to open shut to the point of requiring the unit engineseers to spend time with it back at base, being beyond repair in the field.

The Orks may or may not be able/willing to attempt to spin the locking wheel to unlock the hatch, and then it's a moderately difficult effort to overcome the locking mechanism, and the PCs can attempt to counter the rotation from the inside, but they're unlikely to break their handholds doing that. At that point, it's an unlocked hatch that the PC's can attempt to hold shut, probably with a bonus because they're pulling down - and thus the Ork trying to pull it up and open has to lift them as well.

They can certainly attempt to carve the hatch open (and, honestly, that's probably the Orkish preference), which is likely easier than going through the hull, though still not actually big enough for them to fit through, but big enough to shoot/toss a grenade through. Pulling numbers from thin air, let's call it doing 1/2 the relevant Armor Value damage past the armor when targeting the hatch to damage the locking mechanisms, then another 1/2 if they want to completely break the hatch to the point where they don't need to pull on the hatch any.

Funny how Power Klaws are the answer to just about every problem, when you're an ork.

Power Klaws: The cause of, and solution to, all of life's problems.

Funny how Power Klaws are the answer to just about every problem, when you're an ork.

Very true.

Somewhere there is a Mekboy trying to build a gun that shoots Power Klaws. The collateral damage as a side effect of this project is extensive.

This is actually the driving factor to all of the Wars for Armaggeddon.

They are just about getting enough materiel to make this happen on a large scale.

A -30 to rip open a tank hatch is even mild. I think -50 or -60 is more appropriate, this is practically impossible without tools.A Nob might be able to pull it off (pun not intended, but still kept), but most ork boys would try in vain before hacking everywhere with choppas and possibly damaging something.

As for the comments on weak spots: No it is not needed to have rules for weak spots just because they exist. The system is an abstraction. Humies have weak spots too - if you try to damage the eyeball you can easily do that with a finger or a twig, while the rest of the human is pretty much immune to poking damage.

The commander's hatch does not have to be heavily armored - an AT hit is unlikely to hit there, unless a grenade is used. And tanks are notoriously vulnerable to top attack in RL too - in ww2 planes with autocannons would destroy many a german panzer, and modern AT missile system like Tow launchers use top-based attacks.

The rear hatch is really a door though, as I would think it is as heavily armored as the rest of the rear armor, which means it's only real weakness are the hinges or whatever holds it on. It's also more exposed, so more likely to be designed not to easily open from the outside when locked.

And also keep in mind tanks have vision slits that by nature is not as well protected as the armor itself - they may be shot and destroyed or smashed, making the tankers blind. Smart AT tactics can render a tank virtually harmless if you have completely access to the top.

In other words, you don't want a mob of howling orks on top of your tank. That's what the infantry is for.