Dragoon,
Aside from the para role assigned to a single rifle company (and selected combat support attachments if the unit is creative with its allocation of para positions), there are no doctrinally-formalized "sub-specialties" for the other 2 rifle coys within a light battalion. To the best of my knowledge, the assignment of such "specialist roles" is confined to 3 PPCLI at the present time.
The idea is to give the non-para rifle coys a similarly specialized light infantry role which fosters a sense of sub-unit identity while offering capability benefits the battalion as a whole. When I served in 3 PPCLI a couple of years ago, A Coy was para, B Coy was Mountain, and C Coy was Amphibious and Airmobile. These mobility-related SME tasks give each sub-unit a focus above and beyond their core light infantry skills. "Core" battalion-wide skills within 3 PPCLI include operations in complex terrain (urban, forested, etc), so there is no requirement for sub-unit specialization in those "bread and butter" areas.
What the coy "specialites" amount to is the assignment of suitably-qualified soldiers to that particular sub-unit, combined with a coy-wide focus on researching, training for, and performing the assigned secondary role in support of battalion operations. To use the B Coy "Mountain Ops" example which I alluded to in the Para thread, when I was with the Coy we had the majority of the unit's Mountain Operations Instructors (MOIs) employed within the coy ORBAT. We did all of the "common-to-all" light infantry training that the other coys did, but above and beyond that we:
- conducted the annual Basic Mountain Operations School for the remainder of the unit (90% of 3 PPCLI personnel are B Mtn Ops qualified. Everyone joining the battalion attends the course as a "welcome to the battalion". This program served us VERY well in the mountains of Afghanistan),
- provided SME MOI support to the other 3 VP sub-units for their internal training,
- provided SME MOI support to other 1 CMBG units,
- provided SME field-force representation to the CPC Mountain Ops Cell,
- were the obvious choice to conduct a SOVEX in the moutainous terrain of the Yukon adjacent to Kluane National Park,
- conducted pre-course training for 3 PPCLI MOI candidates,
- facilitated the movement of other 3 VP sub-units over mountainous terrain during tactical exercises by day and night. B Coy did this by constructing, operating and securing the applicable installations (scramble lines, single/double/3-rope bridges, vertical hauling lines, suspension-traverses, rappel sites, etc).
C Coy performed similar functions in regards to amphibious and airmobile operations. They also picked up the additional task of being the battalion Non-Combattant Evacuation (NEO) SMEs while 3 VP had the Army's NEO task. This was based on the fact that such operations would most likely occur in an airmobile or joint amphibious context.
Since I left 3 VP in late 2002, my understanding is that C Coy re-roled a year ago to a "Long-Range Patrol" focus. The idea being that with the NEO task passed to another unit and the majority of 3 VP personnel VERY familiar with airmobile ops from Afghanistan, C Coy could focus on a new area of light infantry expertise. It made good sense. Now that C Coy is adopting the Para role, it remains to be seen whether A Coy will rejeuvenate the amphibious/airmobile specialty, or continue the LRP focus started by C Coy. It is entirely the CO's call, since none of those secondary sub-unit tasks are mandated by higher HQ.
I can't speak to what 3 RCR or 3 R22eR do internally WRT sub-unit "specialties", but I can say that the approach works exceptionally well within 3 PPCLI. It is a "good thing" for a whole host of reasons, not the least of which is the sub-unit focus/cohesion that such an assignment fosters. Add to that the specialized light infantry skill-sets and concentrated subject-matter expertise that the sub-unit roles generate, and you have a win-win situation.
I hope this answers your question.
Cheers,