You can only libel individual or individuals who can clearly be identified as the target of the allegation. An allegation against a general group is not a libel, even thought it may be untrue, and even though the general group is clearly defined.
Therefore to write that "soldiers of the Loamshire Regiment murdered prisoners of war" cannot be a libel as (even though the Loamshire Regiment might be but six hundred men) as no individual or individuals can be clearly identified.
However writing "A number of Senior NCO's of the Loamshire Regiment murdered prisoners of war" can't be a libel as "A number of Senior NCO's" is too vague as these might be any of the RSM, the several CSM and equivalent ranks such as CQMS, the Colour Sergeants, the Staff Sergeants and etc..
But as that identity doesn't has to be by direct naming as long as that individual can still be clearly identified even though they were not named. Therefore writing that "The RSM of the Loamshire Regiment murdered prisoners of war" can be a libel as there is only one RSM. And he can be identified.
Hope it helps explain the law...