This can be tricky because in different situations the answer is different:
In this specific example, the 'continuing to wound' is not an issue. The basic question the
OP is making is this: does the cannon need to deal 1 wound to kill a model or 3?
Pure RnF units: In this example, the unit has 2 wounds on it already so only 1 wound is required to remove a model. The positioning of the shot and the models in this example is such that after it kills a model there are no other models from the unit to be hit. As per the 'excess wounds are lost' wording, the cannon can roll 1-6, only 1 is required to remove a model, the excess (if any) are wasted. The reason you only need to deal 1 wound to remove a model has been clearly stated in that the unit has 2 wounds on it and only 1 more wound is required to remove a model. Wounds are allocated against the unit as a whole and are added up until a model is killed (removed). You can place 2 wound markers on ogre D however the 2 wounds are on the unit as a whole and only 1 more is required to remove a model, regardless of the direction/specific location of the shot. Because cannons (and bolt throwers for that matter) specifically state that you check to see if the model is removed before continuing, you only have to deal 1 wound to remove a model and the shot will continue. If the cannon shot in this example were to have come from the side and therefore would continue to hit and wound more models, you would need to roll 3+ to kill the next model, any excess are wasted, and so on until the cannonball fails to remove a model, the bounce distance is reached, or the unit is completely wiped out (and the bounce distance would not bring it into contact with another unit).
Mixed units: Cannons and bolt throwers basically have the ability to 'snipe' or target specific models within a unit as the shot hits and kills in a direct line. If the unit contains anything special (Unit Champion or Character) AND the shot would hit one of these special models, the above
RnF rules WOULD NOT apply. You would be required to deal enough wounds to kill the specific special model hit by the shot. If the shot were to hit a
RnF model prior to hitting a special model, the
RnF wound allocation would apply (only need 1 wound to remove a
RnF model), then you would be required to deal full wounds to the next model (regardless of whether it is special or
RnF).
Look Out Sir! If the shot would hit a special model you may make a look out sir roll to see if a
RnF model 'jumps in front' and takes the wound instead. If a successful
LOS roll is made, the
RnF wound allocation would apply (only need 1 wound to remove a
RnF model), then you would be required to deal full wounds to the next model (regardless of whether it is special or
RnF).
It's important to note that you wouldn't need to make multiple LOS rolls. The character is 'pushed out of the way' (or however you want to visualize it) and the wound(s) that would be dealt to his position in the unit (the Rank and/or File he occupies within the formation) are dealt to a RnF model (pulled from the rear) and the continuation of the shot goes to the next model in natural progression of the line of fire. The only time this could get tricky is if there are multiple characters next to each other or if the unit consists of only a Character and one other model. In the former, you would need to make one LOS roll for each character if the shot would hit him during it's natural progression. In the latter; if the shot would hit the character first, you could LOS it and kill the other model. The character would now have to take the next hit as he is now the 'next in line' to be hit (no one else is there) and the shot has penetrated the Rank (which consists of only 2 models) so both are hit. So, the short answer is that although cannons and bolt throwers have the ability to 'snipe' specific models within a unit, this only applies on a model to model basis
if one of the models hit is a special model. Otherwise, the wounds are allocated to the unit until enough woulds are caused to remove a model; then the next model is hit, etc.
Hope this clarifies the question for ya. I'm at work right now so I don't have my
BRB with me to cite specific page numbers but the
RnF wound allocation can be found in the section regarding allocation of wounds from shooting and the
LOS rules can be found in the section about taking saves/
LOS rolls in the shooting section.
-Skrog