These are the most generic ways of helping out the countries involved, but some of them could be the hardest to achieve.
How would you go about achieving these to the best of the countries' involved abilities, P?
Infantry doctrine requires war experience by someone or other. Making it consistent requires a powerful training inspectorate. The British had different training systems all over the shop until Maxse turned up, for instance. So I'd say the best time to institute it is during Haldane's reorganisation of the army, with someone pointing out that in the event of a war Britain will have to scale up to a "million man army". Germany has a reasonable system, IIRC, but needs it to be more rigorously enforced, so that means cutting back on the power of battalion commanders, I suspect, and enforcing a top down system of training. France I need to do more reading on; ditto everyone else.
Someone needs to learn the lessons of the R-J War and really start churning medium and heavy artillery out. The French and British are especially weak here. The French because the 75 manufacturers are greedy and the British because they have a tiny army. Someone needs to get the RGA (Royal Garrison Artillery) to point out that in the event of a trench war, their mathematical and siege skills will be at a premium. Again, Haldane's tenure is probably easiest, although Boer War reforms are possibly also a good time, what with "Long Tom" and so on still in the public consciousness.
Trench mortars aren't a requirement for the Germans, who already have them, but they're essential for the British and French, who otherwise have to improvise sub-standard kit. Again, the R-J War seems a good occasion to have someone realise that infantry effectiveness will be enhanced if they have organic mini-artillery.
The same goes for machine guns. They are useful both defensively and offensively, since they can deny ground and perform barrages to cover an advance. They are ammunition hungry, and this will upset logistics types, but doubling their numbers will result in a very effective infantry.
Grenades and Rifle Grenades are a bit trickier, so I'm going to say Boer War or R-J War again, probably the latter. IOTL everyone assumed they were only for siege warfare, so the Germans stuck them in fortresses, and the British issued them to the Royal Engineers, which is useless to the infantry, really. However, the Germans had huge stockpiles they were able to redistribute swiftly. If the British have more paranoia about invasion, they could stockpile some in new "Martello Towers" or somesuch, and then send them out once the situation becomes clear.
LMGs or SMGs at low level requires both recognition that the RoF of a rifle is too low for close combat and acceptance that a section commander can be trusted with the responsibility of such a weapon. The Germans have a very easy time of this, since their NCO structure was very rigorous.
Light tanks, heavy ones and armoured cars can all sit in the same bracket. Although they sit in different spots both tactically and strategically. ACs are better for scouting and you can probably work light tanks into this, too, as up-armoured ACs. Heavy tanks mean one assumes any penetration of enemy lines will be very hard work, and so can either be up-armoured light tanks or completely new designs produced as infantry support weapons. Again, R-J War as the inspiration.
Better training for NCOs and low level officers means a recognition that the war will be low level. Tie this into increasing organic support for battalions and you've got a winner.
Even in countries with annual manoeuvres, they were too frequently rendered frivolous by interfering monarchs and the like. FF demanded a grand cavalry charge during the AH manoeuvres of '12, IIRC, and the Kaiser forever messed about with the German ones. The British manoeuvres of '12 are an example of a different problem: that while one army had a full peacetime staff (Aldershot), Grierson's chaps were a scratch formation. That should have showed the unreasonable nature of the situation, but Grierson succeeded despite the obstacles, and the problem was obscured. The French have similar problems in that their army/corps level headquarters are in their infancy compared to the Germans. That's because of governmental insecurity about the army's loyalty. Fix that sooner and there's more time to fix French problems.
Better communication between infantry and artillery means lots of telephone wire, telegraph poles, flares, semaphore, runners and so on. I honestly don't know how to put this in place pre-war. I suppose more evidence of exposed forward artillery being shot up in by infantry in a recent war, but even that might just lead to artillery being withdrawn to division command, further complicating things. I suspect the French have a fairly simple way around this, as they can claim it's a return to Napoleon's "battalion guns", and just attach the guns directly, then realise the dangers of them being up front simply by observation during exercises, and start working out communications systems pre-war.
Demands an awareness that there will be huge trench battles. There were lots of shells pre-war, but everyone stockpiled shrapnel, which was no use if it buried itself in mud. HiEx will pulverise everything. Again R-J War lessons is the way to go here. Sheer numbers of shells requires Kitchener types who recognise the war will be long. The Russians did realise they needed more shells, but IIRC they simply couldn't afford to bring the army up to that level of preparedness in peace, so they're perhaps a bit shafted.
More advanced aeroplanes simply means more chaps throwing money at them. An interruptor gear developed pre-war would go a long way to ensuring that once the Entente gain air superiority over the Western Front, they never lose it.
A sensible look at whether one should be in the army is tricky. It's something that seems obvious in retrospect, but not at the time. Even at the time, a manager complaining that his men have gone off to the army will look unpatriotic, so I'm not sure. Maybe someone like
Geddes for the British, as he's very forward-thinking and has a good strategic brain.
Perhaps no "Cult of the Offensive" could help for #2 (and maybe #1?), and these could both be helped by one possibility for #3, which is a consistently strong Radical government in France for 1905-1914? It appears the Radicals did pretty well in that period, and the Radical Doumer came close to achieving the Presidency in 1906. That way you could (at least, as I understand it, someone please come along to correct me!) have a completely Radical government from 1906 to 1913. Even better if you get a Radical to win in 1913, but by that point you've given the army and navy seven years of consistent budgets.
I rather like this idea. There's always the problem one'll lose some good commander over politics (Catholics distrusted, for instance), but a good strategic plan in the first place should make up for that.
Not sure how you would achieve #1, but perhaps keeping Bernhard von Bulow as chancellor would help, seeing as he had at least served in the army, and seems to have been on relatively good terms with the Kaiser, as well as being willing to say "no" to him?
#2 is a staff-issue, going about it might be tricky, though.
#3 is up in the air. For ease (and desire for capital ship actions), it might be easier to pick the "use it" option. How would that be different from the case in OTL, P?
I suspect that #1 is tied to making German politicians grumpier with the army. So a disaster (like Isandhlwana was for the British) or two might be enough to get a consensus that the military needed more civilian oversight. Failing that, having the Kaiser actually bother to check what was possible before war broke out could well result in his demanding two war plans, solving #2, and if he has a row with the army chief, he can then institute #1. I'm wary of this, because he was generally deferential to the army, but I'm not aware of anything other than these two routes.
For the navy, she did succeed IOTL in tying down hundreds of thousands of Brits in defensive positions in the UK or in supporting the Grand Fleet. But the capital ships, post-Jutland, don't really do much. More harassing attacks on British towns are my thinking. A determined attack on the BEF crossing could be good, too. Even if it doesn't succeed, we're bound to see more army casualties, and a feeling that the Channel isn't safe, which may well push transport duties further west, making supply lines longer.
#2 seems to be a case of someone figuring it out earlier than in OTL, or was the convoy system really just that unheard of in 1914?
No idea for #1...any help on this?
No, it's about early on. I think the convoy system was tested in the Med '14 or '15, but the Navy ran some numbers
badly, and so thought it wasn't cost effective. Replace the chap with the maths problem ITTL, and bingo!
For a mass army, you need a Kitchener type. The major problem is politics. Getting widespread pre-war acceptance of the idea of sending off millions of voters to die for a foreign country is going to be all but impossible, so I'd have someone doing all the work secretly - a Henry Wilson type - and then present it as a fait accompli. So subtly ready garrisons up and down the country, form corps of retired officers and NCOs who voluntarily keep up to date on tactics, and who can provide modern tactical instruction.
#1 shouldn't be too hard: wasn't the non-acceptance of armored cars in OTL due to some fluke like the KuK not liking the ruckus they made?
#2 and #3 require better cooperation with Germany. Conrad von Hotzendorf isn't in overall command, but perhaps he is arrayed against the Serbs (his nemeses) and is given more troops with which to conduct his personal vendetta. Who is in charge of the Austrian General Staff instead of Conrad? If we have a range of options, who is going to work with the Germans best? What is their plan in the East going to be, if the Germans intend to strike East while the Austro-Hungarians commit more troops to the Serbian front?
Aye, as Kabraloth says, #1 was an unlucky incident. For the others, Conrad isn't a bad chap; it's just that his strategic vision ignores tactical difficulties., and he's got that Redl chap passing stuff to the Russians. If you want another fellow, I'm not sure about '14 seniority, but Archduke Friedrich ran the AOK to December '16. In terms of other high ups, you've got a choice of Rohr, Archduke Eugen, Potiorek (whom I killed in PlC), Dankl von Krasnik, von Auffenberg-Komarow, Archduke Josef Ferdinand, von Frank, and Archduke Josef. I'm not well read on the Austrians, so I can't say who's good. I remember liking
Dankl, but I honestly can't say how he stands up to the others.