IIRC, In the old House Steiner Sourcebook, that's mentioned as their set up. It's also what the CCAF does as well.
As does the FWLM and most other Inner Sphere militaries.
An older source, and explicitly overruled by later sources where the universe is more developed.
Not overruled at all.
Indeed, my response was directly tied to
drjones's reply that "the BT universe (or at least early publications) didn't seem to really distinguish between first and second lieutenants; there seemed to be a flavor of one grade of lieutenant (i.e. lance commander). That actually leaves some room for the idea of "all MechWarriors are officers" as it leaves room for "MechWarrior" as O-1 with "lieutenant" as O-2." So, quite germane within that dialogue, thanks. But, it is a good idea and way through things regardless on his part.
So, if we are talking about early sources, then the early sources are clear lower-level enlisted troopers pilot BattleMechs. Many of the second and third generation unit/scenario sourcebooks include sergeants as lance-seconds, and the Warrior Trilogy is perhaps notable in its treatment of AFFS MechWarrior institutionalization.
Now, having said that: is every graduate of a Inner Sphere military academy a commissioned officer?
Field Manual: FWL (FASA 1699) explicitly states so in conjunction with the Allison MechWarrior Academy (p. 28) and one assumes this rule carries on through the other academies (and similar institutions in the other major states). Which means that, at least in the 3020s-3050s, there was an additional codified pipeline for MechWarriors (like the Hero Academy or Davions Training Battalions) which would thus become the source of "enlisted MechWarriors". I personally believe so--this is borne out by subsequent RPG fodder--so this question is, in a sense, rhetorical. Taking
Rolling Thunder (FASA 1651), for example, into account, we know that sergeants exist in the FWLM MechWarrior arm, and that academy graduates (such as Mikhail Cherenkov and poor Esteban Rodriquez) are subordinate to non-university MechWarriors (such as Lucas McCain)--and that academy graduates themselves can be sergeants (such as Peter Jensen). Vexing, to say the least.
Now, the Waco Ranger's inclusion of the rank of MechWarrior Sergeant was notable (see
The Mercenary's Handbook, FASA 1616, p. 86, 89). For context, the ELH of 3025 did not use the rank of Sergeant for MechWarriors (but did elsewhere for conventional arms, so the omission was not due to a lack of understanding on the author). Little of the fiction/prose provides substantial clarity because it rarely involves the interaction between the various arms at an interpersonal level (and it is written by non-veterans in large part, at least until relatively recently, who might well have had little drive to highlight such an event). Many mercenary outfits use sergeants (Wolf's Dragoons, the Kell Hounds, Northwind Highlanders to name but three prominent ones--see
The Fourth Succession Wars Scenarios, Volume 1 (FASA 1654)--as well as the AFFS, LCAF, and DCMS (the latter of which is more sparing--see the rank of Master Sergeant in
House Kurita: The Draconis Combine, FASA 1620). The CCAF uses only commissioned officers to pilot 'Mechs (the implication here being akin to
drjones's interpretation of the O1/2 split for Sub-Commander/Commander ranks).
EDIT: The LCAF does indeed use Leutnant as an interim rank for MechWarriors--it is effectively a cadet-ranking, like midshipman in the Age of Sail--with the actual lieutenants being First Leutnants that would then be in official command of a lance/platoon. But the use of Sergeant has occurred in canon, so it cannot be dismissed outright (see FASA 1654, p. 28 as one example).
