How Many BattleMechs Exist in 3025?

[Edit: more exact estimates on Aug 10, 2017 /Edit]

I estimate a ceiling of 54 thousand BattleMechs.

383 regiments employed directly by the Successor States
(plus 744 regimental and 1152 battalion command lances)
24.83 regiments known to operate in the Periphery
(plus 18 regimental and 22 battalion command lances)
3.2 regiments estimated among lesser, unnamed Bandit Kings
2.75 estimated merc regiments otherwise (un)employed
11.5 regiments estimated under corporate control
5 potential regiments of unlisted FWL provincial forces

[Edit, Sep 1, 2015: but see also this post. /Edit]

Such an exact accounting of forces might seem restrictive to some people. But like the Kurita house book says:

Although efforts have been made to gather the most up-to-date information possible on the forces, readers must remember that regiments are constantly being reformed, transferred, temporarily removed from active service, reactivated, or decommissioned for spares.

Especially with mercs, there's a constant churn of big units fragmenting into little units, and little units joining up to reform into big units, so there's plenty of room for a Player Unit of just about any size and type to form up in just about any part of the Successor States.

Details below the jump.


Line Forces Listed in the 3025 House books:

Accounting for understrength and overstrength units, and including mercenaries, I count approximately...

Kurita: 82 'Mech regiments ("about 80" vs. 80 in MW1e)
Davion: 115 'Mech regiments ("over 110" vs. "about 110" in MW1e)
Liao: 51 'Mech regiments (unspecified vs. "barely 60" in MW1e)
Marik: 59 'Mech regiments ("approximately 60" vs. 40 in MW1e)
Steiner: 75 (75 + 1 company vs. "slightly over 75" in MW1e)

Marik gains quite a few regiments, probably to account for provincial forces outside of federal control. It also makes them a less appealing target for the 4th Succession War.

Davion gains 5 regiments while Liao loses 9. I wonder if that was deliberate, to help set up the 4th War? I wonder also if the change reflects Davion drawing mercenaries away from Liao, or the loss/seizure of a factory (the Kallon plant on Talon, maybe, or Asuncion and Bernardo or Carver IV).


The Periphery:

Again accounting for unit strength and including mercenaries, I count:

Taurians: 10 'Mech regiments
Canopians: 6 'Mech regiments
Outworlders: 1.33 'Mech regiments
20 Lesser Kingdoms and Alliances: 7.5 'Mech regiments

MW1e says that the fragments of defeated or mutinous 'Mech units flee into the periphery, that some emerge as Bandit Kings after a few years, and that more than 60 such bands exist by the year 3000. The Periphery book names only 20 lesser polities (not all of them bandits), assigning them 30% of the 'Mechs known to be operating in the periphery. Since I like fractal symmetry, I'll estimate the total force of the 40+ remaining bands as 30% of all bandit 'Mechs. (7.5 known regiments / 70% = 3.2 regiments across the 40 unnamed bands. Which, conveniently, comes out pretty close to the average size of a player unit.)


Mercenaries:

I count a total of 94.5 mercenary regiments in the House books: 88.5 in the Inner Sphere and another 6 in the Periphery. This is pretty close to my old estimate of 102 regiments (which was based on the ratio of MW1e House regiments to TR:3025 notables).

2 units have five or more regiments
3 units have four regiments
7 units have three regiments
4 units have two regiments
1 unit has a single regiment of four battalions
29 units have a single regiment of three battalions
8 units have a single regiment of two battalions
19 units have a single battalion
1 unit has two reinforced companies
2 units have a single company

Supposing these 70-some battalion+ sized units are the only battalion+ sized merc units extant in 3025, then based on the distribution of player unit sizes I calculated a few entries ago, and the "Determine Affiliation Type" roll in MW1e, I'd expect there to be about 25 merc units of company size and about 125 smaller merc units, totaling another 10 regiments' worth of mercenaries.

So why don't all these units show up on the House deployment tables? The Periphery, Liao and Steiner books are certainly detailed enough.

Well, here's an interesting thing: I count 80.67 House regiments for Davion, while the book claims only 78; I also notice that a Liao House regiment (Devon's Armored Infantry) and a Kuritan House regiment (the Legions of Vega) are said to contain mercenaries. So perhaps these smaller merc units are being used to shore up House line regiments (and therefore don't need to be counted separately from those regiments).

House Davion employs 37% of the big mercs named on the deployment tables. Assuming that ratio holds for smaller mercs also, and that 2.67 regiments' worth of smaller mercs really are shoring up Davion line units, then about 4.59 regiments' worth are doing the same in the other four Houses (7.25 regiments total).

I assume the remaining 2.75 regiments' worth of small units are either on the TO&Es (Snord's Irregulars and Marshigama's Legionnaires), unemployed (like we see at the beginning of the novel Mercenary's Star), or employed by rebels (the rest of the novel) and other private groups.


Near-Mercenaries:

As an aside: MW1e notes that more and more regular units are becoming mercenary or near-mercenary units. It elsewhere mentions that more than 55 of Davion's regiments are mercenary, while the Davion House book claims only 34-37 merc regiments. Perhaps near-mercenaries make up the difference.


Corporations:

Based on the disposition of private security forces in the Marik house book, I'm going to assume every 'Mech manufacturer has a private security force averaging a bit over 40% of their annual production. I've already pegged the Inner Sphere's total annual production as 2700/yr, and for now I'll guess the Periphery's at 170/yr, for a total of 11 regiments of 'Mech security.

Few other corporations (a handful of trading cartels, apparently) are big enough or hazardous enough to require a permanent 'Mech security force. Since the Marik book left about ten 'Mechs per corporation to cover non-'Mech sites, I'll estimate these at five corporations with ten 'Mechs each, for a total of 1.4 battalions.


Nobles:

In BattleTech's neo-feudalism, military commanders are awarded lands and titles in exchange for fealty and service, so noble household troops are mostly already known and accounted as part of each House's line regiments.

The Lyran throne is guarded by two 'Mechs from the Archon's favorite unit. Kurita's "palace household guard" (the Otomo) is a mix of units "from Sword of Light regiments and other units from each of the five military districts." The Liaos use the Red Lancers regiment as their household guard. Davion's "Brigade of Guards" is referred to as Davion's household troops. The Ducal Guards of all the major Free Worlds sub-states are listed as line regiments, the 17th Skye Rangers are Aldo Lestrade's house troop, the 17th Rasalhague Regulars seem to be Duke Ricol's, and the Mercenary's Handbook even uses "household regiment" as a synonym for "House line regiment."

When nobles do reserve personal 'Mech troops for private use, the troops seem to be either mercenary (as with Uncle "Chandy" Kurita) or corporate (as with the Duke of Irian; and, I suspect, the Duke of Kathil's Capellan Dragoons). Privately funded units - the New Ivaarsen Chasseurs, the Night Stalkers and Stapleton's Grenadiers - still serve as House line units and weren't raised without the House Lord's permission. (Units raised without permission presumably count as either rebels or mercenaries.)


Private Militias:

So what about private 'Mech units which have the Lord's permission yet don't serve as House line units? (Planetary militias, basically?)

Well, MW1e implies that planets and nobles don't have 'Mechs outside of the House garrison. The Steiner book backs this up, with any 'Mech presence coming from a nearby House regiment; the Liao book backs it up too, with the level of detail pretty well excluding any such forces; the Kurita book is not specific, but the intent seems to be that the force listings contain all known 'Mech forces; the Davion and Marik books are less straightforward.

The Davion book explicitly declares that worlds do raise their own 'Mech forces - these comprise the March Militia RCTs, which are known and accounted for. Davion worlds also have Planetary Guards, which are "regiments - usually infantry - raised from a world's population to serve as a last-ditch line of defense." At least three of these units (Chisholm's Raiders, the Aragon Borderers and the Kittery Borderers) have been enlarged to include 'Mechs. I can't be sure they're the only ones to include 'Mechs, but I'm inclined to think they're meant to be; and in any case, there can't be many others, which would all be substantially smaller, so I'm comfortable accounting any more as drawing from the small, unassigned mercs I calculated earlier.

The House Marik book accepts planetary and provincial forces as a matter of course, but only the largest militaries (and the very tiniest) get detailed. Of the provinces named on the "Voting Blocs" chart, I suspect that only Tamarind, Abbey and Mosiro might not be already contributing to known regiments. To these I'll add Ohren and Zion, which are also described among the "larger and more influential territories," and I'll estimate all five at a half battalion each (a little bit smaller than the smallest force given on the FWL deployment table).

And then there's New Assam, the tiniest province in the FWL, which consists of a single continent on an otherwise Regulan world. It has a single representative in parliament and an army consisting of three regiments of infantry, four batteries of mobile artillery, and two battered Wolverines. If I assume the remaining 130 provinces also have at least two 'Mechs each, that's another 2.4 to 4.4 regiments of 'Mechs, for a total up to about 5 regiments of unlisted provincial forces.



Notes:
Final Estimate: actually calculated at 54046.6 'Mechs but, you know, significant digits take it to 54000. If we assume that only half of all units have converted over to independent command lances, then the final tally would instead be right around 50 thousand.
Command Lances: per BattleForce 1e, each battalion has a command lance, and each regiment has two-lance command element.

All five Sword of Light Regiments: 4 battalions each
25th Rasalhague Regulars: listed on DCMS deployment table, but not in regimental descriptions
1st Proserpina Hussars: 4 battalions
2nd & 3rd Proserpina Hussars: 2nd listed in regimental descriptions, 3rd on the DCMS deployment table; I've counted one as a typo for the other
Amphigean Light Assault Groups: counting these as mercenaries
Wolf's Dragoons: Zeta Battalion, Black Widow Company, and a two-company support group not listed
Draconis Elite Strike Teams: unlisted and unknown, likely no standing 'Mech forces

3rd Davion Guards RCT: listed in regimental descriptions, but not on AFFS deployment table
33rd Avalon Hussars RCT: 4 battalions
42nd Avalon Hussars RCT: 5 battalions
1st Crucis Lancers RCT: counted as 2.33 battalions due to having "so many gaping holes"
2nd Crucic Lancers RCT: counted as 2.33 battalions due to serious damage
3rd Crucis Lancers RCT: 4 battalions
2nd Ceti Hussars RCT: counted as 2.33  battalions due to recent casualties
2nd New Ivaarsen Chasseurs: 4 battalions
1st Kestrel Grenadiers: 2 battalions
1st Aragon Borderers: 2 battalions
1st Capellan Dragoons: counted as 2 battalions because "seldom up to full strength"
1st Kittery Borderers: counted as 2 battalions due to similarity with Aragon Borderers
Swann's Cavaliers: listed in regimental descriptions, but not on AFFS deployment table
Waco Rangers: already listed in Lyran space, so I figure they're replaced by Swann's Cavaliers

Northwind Highlanders, McCormack's Fusiliers: 2 battalions
Northwind Highlanders, 1st kearny Highlanders: counted as 1.5 battalions due to being "badly crippled"
Trimaldi's Secutors: 2 battalions (third is infantry)
Stapleton's Grenadiers: counted as 2.5 battalions due to long, slow rebuilding
Devon's Armored Infantry: 1 battalion (second is tanks)
15th Dracon: counted as 1.33 battalions because both battalions are understrength
Death Commandos: 1 battalion; not listed
All Warrior Houses: 1 battalion (second is infantry)

23rd Marik Militia: listed on FWLM deployment table, but not in regimental descriptions
2nd Fusiliers of Oriente: counted as 2.5 battalions because 3rd battalion is "seriously undermanned"
4th Fusiliers of Oriente: 2 battalions
All Oriente Hussars: counted as 13.44 battalions altogether, due to being understrength
2nd Regular Hussars: counted as 2.88 battalions, due to "often" being understrength
SAFE's Dark Shadows Battalion: 1 battalion; not listed

No notes for Steiner

Taurian regiments probably not using command lances yet.
Taurian Lancers: each battalion is half tanks
Hyades Light Infantry: counted as 75% air-mobile infantry
Every Canopian House Regiment: counted as 1 battalion
Von Strang: estimated at 1.33 battalions
Brotherhood of Randis: estimated at 11 'mechs ("Less than twelve")
Illyrian Palatinate: "several companies" estimated at 1 battalion
Marian Hegemony: estimated at 2 battalions, due to being "three small battalions"

Periphery manufacturing: Magistracy of Canopus builds "less than" 60 'Mechs/yr to maintain their 6 'Mech regiments; extrapolating that ratio to the slightly more than 17 total regiments of the Periphery Houses yields approximately 170 'Mechs/yr.

Duke Ricol's household troops: There was one full Kuritan regiment deployed to Verthandi plus elements of three more -- four regiments is too large a force to all be considered Duke Ricol's "household" troops. However, I notice that the old House Kurita sourcebook has a Duke Ricol commanding the 7 DCMS regiments of the Kirchbach prefecture, and that the prefecture's capital is the homeworld of the 17th Rasalhague Regulars.