My impression of the Army is somewhat at odds with the description.
Really, I don't think its as proffessional as its being portrayed, its certainly no PIRA. It doesn't have access to external training or finances which means its skills and tradecraft are self tought, just as PIRA's was in the 70's.
Its worth noting while PIRA achieved some of its most notable successes during this period (Warrenpoint for example) it also suffered an extremely high level of attrition because activity any activity is observable, this is especially true when your tradecraft is particulalrly hot or self taught.
Oh and unknowns only remain unknown if they stay out of sight, I guarrantee if a member of the Army were to start regulalry observing SAeS establishments for example they wouldn't remain unknown for very long.
Which means the armies activities have to be really low key passive observation. In otherwords the Army is pretty much a wet squib, they have information they simply can't act upon it without Special Branch/PISCES giving them a thorough going over.