I'll give this a shot, using a post from the main forum
and your three premises
- the Inner Sphere is likely to outnumber us,
- our logistical basis might be at risk during these fights as it will be a long run between here and there;
- we have better soldiers and better weapons and let's assume it stays this way.
First, we'll say that there's a kind of 'meta doctrine' as each Clan has their own general take on warfare and trying to cover all those aspects would need some SERIOUS writing and research. But being at the short end of the numbers stick and the nature of combat in the Battletech universe as a whole (where big clashes and large numbers on both sides are fairly rare) then the Clans would go for a kind of 'meta doctrine' that would probably very heavily resemble blitzkrieg.
Blitzkrieg is all about hitting a weak point or a unit with numbers, speed and firepower on your side. You splinter that force so badly it either gets bulldozed aside and is rendered combat ineffective, or it gets broken up, and then the scattered units are in turn cut off, surrounded and destroyed or forced to surrender. And this is all done with close coordination between recon forces who guide the main units to the weak point or unit.
What we might actually see is something more akin to the current Mongol Doctrine which puts a huge emphasis on speed and aggression. The Mongol doctrine seems to be maximum concentration of force on a very small area, combined with attacks on C3 positions, supply depots, all carried out at once. You hit your target with overwhelming force. You shatter them and you deliberately target command Mechs/tanks and you keep hitting, using the speed and mobility that Clan Mech's generally have over the Inner Sphere. The unit you hit is hopefully shattered and scattered, you then press on, emphasising aggression and power to keep the opposing force off balance. By the time that reinforcements have arrived, its too late. You've either moved on, or you're moving on them.
It also seems to emphasise local superiority in numbers, meaning that Zell is out the window and that the Clanners WILL be focus firing you down. Its absurdly aggressive, relying on speed, momentum, the natural aggression of Clan Warriors and their range advantages. Basically its Blitzkrieg + mainlining 12lb of popping candy and 2 gallons of Monster.
This is a contrast to the other major doctrine and an evolution of Blitzkrieg, or Blitzkrieg's brother from another mother, the Soviet concept called 'Deep Battle'.
Blitzkrieg was more tactically inclined with a focus on the battles
Deep Battle was a broader vision with a more strategic bent.
Both relied on tying down enemy forces and punching through their lines with mobile forces to surround and trap enemy forces fighting your initial assault whilst more units moved deeper into the rear areas. The German's emphasis was flexibility at a tactical level, and the Soviets could not match that so instead they went for flexibility at an Operational level (tactical being battlefield, operational being area based) and instead of having flexible SNCO's they used their officers to be as flexible as possible. Note this came about from 43 onwards and they continued to refine the doctrine of Deep Battle until the fall of the Soviet union. They did put it into practice against the Germans during Operation Bagatron.
The Soviet Deep Battle concept also placed a hell of a lot of emphasis on misdirection on a tactical and strategic level (such as was used during Operation Uranus to trap the 6th Army at Stalingrad, and you could argue that Uranus was the first real time the Soviets tried the Deep Battle doctrinal concept, with Stalins approval, after the purges the idea was banished and outlawed, those that still studied it went underground like some kind of cult to avoid the attentions of the NKVD and SMERSH). This would be something the Clans would not like considering their direct sense of combat and the like so the misdirection efforts of Deep Battle would not apply to them.
Deep Battle relied on emphasising your strengths whilst minimising your weaknesses (Concetrating your weight against an outnumbered enemy, not letting your forces get spread out, using operational flexibility if you've not got that good a SNCO/junior officer corps to lead on the battlefield etc) but Deep Battles big thing is that its REALLY hard to defend against it unless you have a large number of reserves and a strong front line force.
Theoretically, the two approaches are different styles of surface-and-gap warfare. Which basically says, attack the enemy where there is a gap (weakness) in his forces rather than a surface (strength).
The Germans exploited gaps through
recon-pull, the Soviets used
command-push.The Germans would send out recon units to find weak spots, and flex their main effort formations to take advantage of and break through them. Recon units found the gaps, and
pulled the main forces after them through the gap to exploit the enemy's rear--encircle him, shoot up his logistics, etc.
The Soviets would say, "I vant gap here," and point to a spot on the map, and they would mass their artillery corps to blow a hole in the line. The command created a gap through overwhelming firepower, and
pushed their forces through it.
The 4th Succession War and the FedCom's attack against the Cappies was a Deep Battle offensive.
Against the Capellans, Hanse was able to outnumber them, out gun them, and had lots of strategic and tactical deception going on and once the main Cappie forces were encountered they were pinned down and more units just jumped past them deeper into the Confederation, this is more Deep Battle than Blitzkrieg. The Fedcom forces were able to mass, crush and push through, especially with the Lyran preponderance of assault heavy units they could also use. And with the Lyrans keeping the Combine busy there was less threat to the north for the Suns so they could deploy more units. Which is why this to me is more Deep Battle rather than Blitzkrieg. Deep Battle also emphasised on punching a hole not in one place, but multiple points and then just flooding through with the forces available when and where somewhere was broke through. With the general assumption that numbers would be on their side, this would then be VERY hard for an opponent to stop. Because if you pull forces away from somewhere else to contain a breakthrough, the Soviets would then try to break through the newly weakened area and so on.
The Clans use Blitzkrieg, and paid as much attention to things like Logistics as the Germans did in WW2. The Clans emphasised flexibility at every level but they used speed and aggression and their own initiative to help them win, this isn't top down. The Clans turn up, land forces and then it seems to be up to commanders on the front how to fight their battles with huge emphasis placed on speed and aggression. I'd say that once they were deployed, even if a full Galaxy was plonked on a planet, the Galaxy Commander would be acting more like a Captain, commanding his or her forces whilst also having an eye on the strategic overview, but one far less than a RCT commander might have.
This is very different to the French doctrine pre-war which was incredibly inflexible in many ways but also flexible in others. Taking lessons from WW1 the French viewed artillery as the god of war and the decisive instrument of a battle. The guns were the weapon of a general or colonel and they decentralized the authority to call in artillery down to junior officers, whilst any very heavy guns were the personal weapon of a Colonel.
With a defensive mindset, the French instead micromanaged the crap out of the battle before it was fought. Fighting out and planning for a battle before it was fought. They would have lots of different plans and the like but they would follow those plans and try make the enemy dance to their well planned tune whilst using artillery to absolutely murder anyone and anything they fought. Of course, this relied on a slow, grinding battle. And was utterly undone by the Germans Blitzkrieg.
By utilizing Blitzkrieg or its Mongol kissing cousin, the Clans would maximise their offensive potential by applying the maximum force to a point. But this would also require the Clans to have a different take on their combat style. Zell and the "YOU! FITE ME! 1 ON 1!!" thing would have to go out the window, because you can't do that with Blitzkrieg. So lets assume rational Clans who whilst fighting each other fight within Zell, the IS forces are Dezgra unless they prove otherwise, so focus fire etc is all fine.
By applying the maximum force at a small area to smash an opposing force and force it to splinter and fall back or be cut off, you maximise the firepower advantage of your tech and superior Mechs as well as the skill of your warriors instead of trying to take on superior IS numbers.
LogisticsWith logistics the Clans could have solved their own Logistical problems if they had not forgotten how to war. Canonically the Clans didn't fight any long campaigns, it was all decided pretty much in an afternoon with one grand punch up. And over a century of this as well as doctrinal bias for it made the Clans largely forget how to do a proper campaign.
Steps taken could have included setting up supply posts and depots on worlds on the Exodus trail or in the Chanline Isles, reducing the supply turn around from 6 months to a few weeks. As was done in MasterArmina's superb Scorpio Ascendant which has helped shape a lot of my writing.
The Clans were crippled by their lack of strategic knowledge and tactical knowledge, they had next to no recon data and it was all done on the fly which is an intolerable way of doing things. Operation OVERLORD wasn't something that was put together by putting men and equipment on ships and then just landing them on the Normandy coast, it came about with years of preparation, a huge build up, extensive intel work and recon, 'dry runs' with operations in italy and africa to build up confidence and awareness.
The Clans load up on dropships, jump in, land.
?? Profit.
And their logistics or lack thereof (see Clan Ghost Bear) represent their own over confidence and lack of strategic understanding. If they had built up stockpiles 'nearby' or even worked together to use their Potemkin's as roaving supply ships carrying food, ammuniton, crated mechs etc etc it would have gone a huge way to easing their logistical burdens.
The Numbers problemThis is one immutable problem with the Clans, they are horrifically outnumbered. With less than a billion people in total and a few hundred thousand warriors in total between all the Clans, there's simply no way they can invade the Inner Sphere to conquer it. Its too big, and the industrial disparity is too great. So to fix this, going with more rational Clans you'd need to go back into their past and have them go nuts for exploration and explotation. have them make colonies on the Exodus road (we KNOW there are habitable worlds there), have them conquer the Tanite worlds and look further afield. Use iron wombs to breed as many people as you need as well as saying to the lower castes "Go forth and procriate." as you NEED babies.
You'd then have to change the Clan's view on Freeborns, have them accept Freeborn as warriors, not as guys who's job it is to clear minefields by running through them whilst being 'encouraged' by machine gun fire from the rear, but recognise their contributions and use them as second line troops with the offer of, if they are worthy of being accepted into front line forces. Raise Freeborn clusters and even galaxies, you NEED the numbers.
This would be fed by the exploitation of worlds and any orbital resources. Mine baby mine! Grab asteroids, strip them bare, a worlds only marginally habitable but is rich in X Y Z material, colonize that sucker.
This would HAVE to be driven by the idea that the Clans WOULD return to liberate the Inner Sphere from its corrupt house lords or conquer it to reimpose the Star League Mk 2. So this would have to be a vision that the Clans are working towards, a return to the paradise of the Inner Sphere, giving the Clans a goal they can work for.
This would probably also mean that the warriors are not quite the absolute pinnacle of their society. Instead the other castes would be treated equally. A 'we all lift together' kind of thing.
https://www.youtube.com/watch?v=mPTCq3LiZSEAnd really, you'd need to keep the SLDF's combined arms approach, but this again only works with a larger population base and a larger military instead each clan having a few thousand warriors, you'd need more. The Clans would have to be more unified and always slowly working towards the goal of returning to paradise, to the worlds their ancestors were cruelly kicked out of by the greed and ignorance of the so called 'Lords' of the Houses.
And even then, its iffy, because you're hugely outnumbered.