Of course there are lots of units with 'rending' attacks or that get extra damage dice (for being a monstrous creature for example) so that would also need to be taken into account....
Then it occurred to me that many units can only glance a target vehicle so we'd need to calculate how many 'Immobilised' and 'Weapon Destroyed' results it would take to glance a vehicle to death and also vehicles inconsiderately have different numbers of weapons on them as well.....
So to cut a long story short it became a more time consuming process than I thought so I didn't bother.....
Which seems like a lame excuse so I have got off my arse and done some of it. This article won't be particularly biased towards Tyranids as the principles are the same for every army.
As every vehicle is at least armour 10, we need to be at least S4 to do any damage so we'll start there.
We'll start off by talking about the chance of destroying a vehicle that you can only glance.
A brief note on Glancing hits.
The fact that a glancing hit reduces the result on the damage table by 2 means that only 5's and 6's give us a particularly useful result.Taking into account that if a vehicle is immobilised then the result becomes weapon destroyed and if a vehicle suffers weapon destroyed then the result becomes immobilised, even a vehicle with no weapons will need 2 lots of this type of damage to destroy it. Regardless of what order they occur in this effectively gives even the most basic of vehicles 2 'wounds' vs. glancing hits.
I can't think of any 2 'wound' vehicles but I'm sure there are some.
A Rhino would be a 3 'wound' vehicle as we need to immobilise it, destroy it's mighty Storm Bolter and then do one of those damage types again as well. A sponson-less Predator or Leman Russ would be the same.
A Chimera would have 4, A Predator with Sponsons would effectively have 5 'wounds' and so on.
As you can see 'Glancing' a vehicle to death takes a bloody long time as the vehicle damage table is to all intents and purposes an additional 'save' for the vehicle.
Well that's my basic premise, onto the maths...
S4 Vs. Stationary or Immobilised Armour 10 Vehicle.
Auto hit, Needing 6's to glance (glance is -2 to damage)
1 Attack at S4 gives us a 0.167 chance of a glance, 0.056 chance of an immobilised/Weapon destroyed.
We need 35.71 S4 attacks to destroy a 2 wound Armour 10 vehicle.
We need 53.57 S4 attacks to destroy a 3 wound Armour 10 vehicle.
We need 71.43 S4 attacks to destroy a 4 wound Armour 10 vehicle.
We need 89.29 S4 attacks to destroy a 5 wound Armour 10 vehicle.
If the vehicle's moved up to 6" the odds become stupidly low.
We need 71.42 S4 attacks to destroy a 2 wound Armour 10 vehicle.
We need 107.14 S4 attacks to destroy a 3 wound Armour 10 vehicle.
We need 142.86 S4 attacks to destroy a 4 wound Armour 10 vehicle.
We need 178.58 S4 attacks to destroy a 5 wound Armour 10 vehicle.
If the vehicle's moved over 6" the odds reach the ridiculous.
We need 222.22 S4 attacks to destroy a 2 wound Armour 10 vehicle.
We need 333.33 S4 attacks to destroy a 3 wound Armour 10 vehicle.
We need 444.44 S4 attacks to destroy a 4 wound Armour 10 vehicle.
We need 555.55 S4 attacks to destroy a 5 wound Armour 10 vehicle.
The moral of this story appears to be that glancing a vehicle to death is highly unlikely at best* and next to impossible if it's inclined to move about at all, lol.
* A charging unit of Orks still stands a good chance of doing it (up to and including the moved less than 6" point at least) as they can in ideal conditions get 116 S4 attacks before the Power Klaw Nob even gets a look in. Not sure much else can generate anywhere near that volume of attacks though.
This is where shooting gets a big advantage as the speed that the vehicle has moved is largely irrelevant. However, if the vehicle has a cover save for some reason then assaulting obviously isn't effected by it.
Either way I think this is a good indication of why transports are such a good buy in 5th. ed ;-)
However not everything has a wimpy S4 attack. Furious Charging Marines are at S5 and Marines also come equipped with the always handy 'Krak' Grenade which is S6. Even some units that are only S3 or S4 get Rending attacks which can make all the difference.
So, Lets forget about glancing and deal with the fact that only penetration** really counts for anything.
** Insert your own dirty joke here if you like.
As there are so many possible variables - Strength, rending, extra damage dice, speed vehicle moved, vehicle armour value, etc. I'm going to limit this particular post to damaging vehicles that are armour 10 or have a rear amour of 10 (which is the bit the rules say were going to be assaulting). I'll cover killing Walkers and the few higher armour vehicles in another post.
For comparison we'll also look at an equivalent strength ranged weapons chance of damage against the same armour value. We'll also work out the number of attacks to 'guarantee' a kill from a 'Mathshammer' prospective.
S3 rending vs. Armour 10.
Vehicle stationary.
Auto-hit, 0.167 chance of Rending hit, 0.111 chance of pen, 0.037 chance of wrecked/destroyed.
27.02 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.083 chance of Rending hit, 0.055 chance of pen, 0.018 chance of wrecked/destroyed.
55.55 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.028 chance of Rending hit, 0.019 chance of pen, 0.006 chance of wrecked/destroyed.
166.67 attacks required to 'kill' vehicle.
A S3 weapon couldn't harm the vehicle at all unless it also had rending.
Marine Sniper Scout (BS3), Sniper Rifle (S3, Heavy, Rending). 0.5 chance to hit, 0.083 chance to rend, 0.055 chance to pen, 0.018 chance of wreck/destroyed.
S4 rending vs. Armour 10.
Vehicle stationary.
Auto-hit, 0.167 chance of Rending hit, 0.167 chance of pen, 0.056 chance of wrecked/destroyed.
17.86 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.083 chance of Rending hit, 0.083 chance of pen, 0.028 chance of wrecked/destroyed.
35.71 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.028 chance of Rending hit, 0.028 chance of pen, 0.009 chance of wrecked/destroyed.
111.11 attacks required to 'kill' vehicle.
I can't think of any S4 ranged weapons with Rending except Tellion's Bolter and he's a bit to 'individual' to use as a comparison.
We can start ignoring Rending now as any roll of a 6 will result in a penetrating hit anyway once we reach S5.
S5 vs. Armour 10.
Vehicle stationary.
Auto-hit, 0.167 chance of pen, 0.056 chance of wrecked/destroyed.
17.86 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.083 chance of pen, 0.028 chance of wrecked/destroyed.
35.71 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.028 chance of pen, 0.009 chance of wrecked/destroyed.
111.11 attacks required to 'kill' vehicle.
A Marine (BS4) Heavy Bolter (S5, AP4, Heavy 3) would have a 0.11 chance of wreck/destroyed on the same target.
S6 vs. Armour 10.
Vehicle stationary.
Auto-hit, 0.334 chance of pen, 0.111 chance of wrecked/destroyed.
9.01 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.167 chance of pen, 0.056 chance of wrecked/destroyed.
17.86 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.056 chance of pen, 0.019 chance of wrecked/destroyed.
52.63 attacks required to 'kill' vehicle.
A Guard (BS3) Multi-Laser (S6, AP6, Heavy 3) would have a 0.167 chance of wreck/destroyed on the same target.
Obviously at S6 we've reached the strength most likely to be associated with monstrous creatures*** so we'll concentrate on them from this point on with a brief stop for Power Fists at the S8 mark ;-)
*** yes there are some S5 monstrous creatures and I'm sure there is the odd character here and there that can hit at high strength but isn't a Monstrous Creature but I don't want people slipping into coma's before I finish this bloody article...
S6 Monstrous Creature vs. Armour 10.
Monstrous Creature Status gives us Strength + 2 Dice to attempt to penetrate the target vehicle with rather than the usual Strength + 1 Die.
Vehicle stationary.
Auto-hit, 0.833 chance of pen, 0.278 chance of wrecked/destroyed.
3.6 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.417 chance of pen, 0.139 chance of wrecked/destroyed.
7.19 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.139 chance of pen, 0.046 chance of wrecked/destroyed.
21.74 attacks required to 'kill' vehicle.
S7 Monstrous Creature vs. Armour 10.
Monstrous Creature Status gives us Strength + 2 Dice to attempt to penetrate the target vehicle with rather than the usual Strength + 1 Die.
Vehicle stationary.
Auto-hit, 0.917 chance of pen, 0.306 chance of wrecked/destroyed.
3.27 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.456 chance of pen, 0.152 chance of wrecked/destroyed.
6.58 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.153 chance of pen, 0.051 chance of wrecked/destroyed.
19.6 attacks required to 'kill' vehicle.
A Guard Hydra (BS3, Twin Linked, S7, AP4, Heavy 4) would have a 0.50 chance of wreck/destroyed on the same target.
S8 Power Fist/Klaw vs. Armour 10.
Vehicle stationary.
Auto-hit, 0.667 chance of pen, 0.222 chance of wrecked/destroyed.
4.50 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.333 chance of pen, 0.111 chance of wrecked/destroyed.
9.01 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.111 chance of pen, 0.037 chance of wrecked/destroyed.
27.03 attacks required to 'kill' vehicle.
S8 Monstrous Creature or S8 Chainfist vs. Armour 10.
Monstrous Creature Status gives us Strength + 2 Dice to attempt to penetrate the target vehicle with rather than the usual Strength + 1 Die (as would using a Chainfist).
Vehicle stationary.
Auto-hit, 0.972 chance of pen, 0.324 chance of wrecked/destroyed.
3.07 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.486 chance of pen, 0.162 chance of wrecked/destroyed.
6.17 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.162 chance of pen, 0.054 chance of wrecked/destroyed.
18.52 attacks required to 'kill' vehicle.
A Marine or Guard Veteran (BS4) Meltagun (S8, AP1, Assault 1, Melta) would have a 0.343 chance of wreck/destroyed on the same target at short range or 0.222 at long range.
S9 Monstrous Creature or S9 Chainfist vs. Armour 10.
Monstrous Creature Status gives us Strength + 2 Dice to attempt to penetrate the target vehicle with rather than the usual Strength + 1 Die (as would using a Chainfist).
Vehicle stationary.
Auto-hit, Auto-pen, 0.333 chance of wrecked/destroyed.
3.00 attacks required to 'kill' vehicle.
Vehicle moved up to 6".
0.5 hit, 0.5 chance of pen, 0.167 chance of wrecked/destroyed.
5.99 attacks required to 'kill' vehicle.
Vehicle moved over 6".
0.167 hit, 0.167 chance of pen, 0.056 chance of wrecked/destroyed.
17.86 attacks required to 'kill' vehicle.
A Marine (BS4) Lascannon (S9, AP2, Heavy 1) would have a 0.185 chance of wreck/destroyed on the same target.
Conclusions.
Well that's a lot of information I've thrown your way and thanks for bearing with it till the end.
As you can plainly see, transport vehicles have much more to fear from being shot at than from being assaulted.
Look at it this way...
Consider the armour value to be like toughness since you need a decent die roll to penetrate that armour with, its basically the equivalent of a T6 or T7 creature, Call the number of hits required to 'guarantee' a kill it's wounds and you find most vehicles have the equivalent of far more wounds than any character or monstrous creature. Carrying that principle on the vehicle damage table roll is to all intents and purposes a 3+ invulnerable save and any instance of cover we'll call 'Feel no Pain'.
Would you honestly want to try and kill 10 of those creatures in assault...no?...I thought not.
Like it or not 5th. ed. has made vehicles very difficult to destroy and Maths shows us that shooting them to death is more efficient than assaulting them in virtually all cases.
It's no wonder that MSU (Multiple Small Unit) vehicle gun-lines are so popular...
Maybe I should have worked this out before I decided to have all my Guardsmen on foot?
Still I've got plenty of guns so it isn't a complete loss....
Editors Note : It's getting late and I'm yet to double-check the Maths so I'll post it as is and check the sums tomorrow.
