Some people have cited the lack of hit location here as an issue, personally in the majority of cases I believe it is irrelevant and a GM can always simply subtley alter the crit discription to suit the logical possibilities of a blow. (e.g. a leg critical has been indicated... though the attack roll had already been modified to take account of the cover provided by a waist high stone wall... a successful hit still happens, therefore he can't have been hit in the leg..). Many other systems get around this problem by having a "called shots" modifier, i.e. the attack roll is made at a penalty, if you miss you miss completely, otherwise you hit what you aim for.
This methodology can be applied in Rolemaster, you could simply determine the modifiers for attacking specific locations. However, I've always considered the hit or miss called shot rather illogical. What if in attempting to hit an arm your swing is blocked by the body? It makes sense in occasions where you are deliberately attempting to avoid hitting other parts of the body (like shooting a target in the leg to immobilise them...rather than kill them.) but not otherwise.
In most cases I would simply re-apply the modifier to determine the hit as normal and then modify the crit result to suit. Therefore hitting with the modifer means you hit the specifed location (and any crits are modified to represent that location being hit), hitting without the modifier means that any crit resulting from the blow is modified NOT to include that location.
Bearing this is mind we then come to the "Ambush" skill (which I'd rather call the Aimed blow or Precision Strike). This should not be affected by the modifiers to hit a specific area but effectively can be used in the same fashion but to greater effect. Failure indicates a complete failure to hit, a hit indictes a skewing towards a more controlled application upon the specfied target area. (i.e. It has a greater chance of achieving a specific critical result than a called shot)
In my experience, systems need to be built from the ground up to accept the mechanics of hit locations and appropriate effects resulting from using them. D&D and Rolemaster were both built with the idea that damage interpretation was secondary to the results of the die roll. You roll high, you do a lot of damage and the narration of that damage is made appropriately from that result. In that paradigm, aiming for a specific location is a moot point. It is assumed that, when attacking, your character is always going for the most effective strike he can obtain and narrative input from the user prior to the roll has little mechanical affect on the results of that die roll. If he rolls well, he hits a vital location. If he rolls poorly he hits a minor location. What the attacker
wants out of that situation ("I want to aim for the head because I want to cause more damage") is moot. In both cases (D&D and RM) the entire mechanic of attacks and damage is built around this idea from the ground up. Therefore, if you start to add hit location systems to them you must reconcile a number of cascading problems that begin to spread through the logic of the entire game.
By comparison, systems that are readily built with hit location systems must be able to accept narrative input of damage interpretation
prior to any die rolls (they attack a specific location because they want a specific result) and still make sense
after the die roll. This is a mechanical feat rarely achieved in RPG design.
In defense of Ambush, it is generally assumed that hit locations that will cause more damage are more difficult to hit. RM's core mechanic makes this assumption difficult to reconcile because making a location more difficult to hit (imposing a penalty on the attack roll) inherently decreases the amount of damage you're going to inflict. The Ambush skill was designed to circumvent that paradox in the core mechanic by creating a mechanism by which the damage can be altered on the critical level. So, the Ambush is a method by which the attacker can gain some measure of control in situations where hit location does make a difference, it is assumed that by taking extra care a more vital location can be hit in comparison with the frenzied attempts of a stand-up fight, and in the end the actual location hit is still left to interpretation of the final roll results. In that respect it is a good tool for obtaining the effects of a hit location system without the 'mess' of attempting to build a hit location system.
All this is staying consistent with RM's (and D&D's) core assumption that interpretation of damage is done after the results are obtained and that narrative input prior to the attack roll has little mechanical affect on the outcome. So Ambush is a pretty clean way of having your cake and eating it too.
On the flip side, one
could argue that such ability is already assumed in the core combat mechanic and that Ambush is superfluous at best. A character who is attacking from a hidden position is generally going to be less worried about defense because his target is not going to be able to return an attack until the following round. So the ambusher can simply apply his entire OB to his attack (leaving nothing for DB) which is an act that is assumed to happen with each round of a stand up fight. Everyone's OB is assumed to be lower than it actually is because only the foolish or crazy actually attack without some attention to defense. In an ambush situation this isn't the case. So simply by virtue that defense is not as much of a concern until after the attack is delivered the effects of the Ambush skill could be trumped by the simple ability to devote everything to the attack.
Possible evidence of the superfluousness of Ambush is the fact that a lot of what was designed into RM at a very early stage was done so with the primary goal of taking what AD&D did and making it more detailed and more accessible to general PCs. From that perspective, the Ambush skill was designed with the goal of working with the crit system they already designed in order to emulate the backstab ability of the AD&D thief (giving the transitioning AD&D players what they would expect to find) and, as a skill, to be available to anyone who wanted it (living up to RM's claim that it is more flexible than AD&D). The reason I mention this is that any conversation regarding the "realism" or "appropriateness" of any trait in RM must take into consideration that, in many, many cases, the designers were making choices simply based on its association with another system that itself may not have been consistently "real" or "appropriate."
