There are 4 lessons fromWW1.
1. Don't do it again.
2. Move things using the internal combustion engine.
3. Preferably under armour.
4. With as many radios as you can manage.
a. But they did it again.
b. Without horses, that becomes a necessity.
c. Armor seems to have been something of a short-cut, a good short-cut, but the British did not put the work in pre-war to figure out motorized combined arms tactics. Even the Americans seem to have done more in their own 1930s exercises and that army did not even have tanks. OJT in the desert took a long time and was costly. The British army continued to make mistakes in France 1944 that by this date, they should not have.
d. The lesson learned was a technology hobbled one.
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Aside from that there is a general lesson of Opportunity cost. If there is finite time and money which is to say always, then spending either on A) means its not available for B) so if you reequip the infantry with new weapons you cannot afford to buy Spitfires or Chain Home or Carriers or tanks or something.
That comes down to the people who are the ones who have to use the limited time and money they were given. The example I use constantly is; "Do the sailors need ice cream for morale, or do they need torpedoes that swim as they are intended and go bang when they hit targets? Spend the money given and time available... wisely.
As to the specifics. .276 pederson is - a crappy machine gun round. Its performance falls off after about 600m. Around 25% of the on hand ammunition in British infantry division is for the Vickers in the MG battalion. that has an effective range of 2000 - 4000m the latter using ammunition introduced for WW2. ( and would normally be firing in support of 1-2 inf BDE not all three.
MacArthur argument. He was right, you know?
This is an unresolved technological issue. The sort of round that works well at up to 600m and allows for semi or automatic fire is bad at long range automatic fire. That's why today everyone uses two rounds. But today and post war generally everyone used something not an MMG for the indirect fire role at range. But then today at range people move around in bullet proof vehicles so interdiction fire from MGs does not work ( and they move in vehicles initially because of NBC threat).
Ehh. The type of war fought these days has brought back the reach out and touch them with direct fires logic and necessity. There is a lot of terrain and light infantry that needs long distance direct fire ground denial and servicing. Not a lot of the present type target matrices are riding around in BMPs. They are skulking about as light infantry. Mortars are good, but MMG and HMG weapons are good too.
If you can get an infantry weapon that can fire semi or full auto out to 400-600m that may be useful but to do that you need to invent the assault rifle and ideally a smaller round so you can carry more.
Settle for infantry brawl distance and let the machine guns do their work.
The Infantry section generates its firepower from the BREN, not the rifle so improving the rate of fire of the rifleman is at best of marginal use. One trick possibly missed was issue of cheap scopes to riflemen, but the marksmanship training in the british armhy ( or US) was more rigorous than the german, so the marginal increase may not have been worthwhile.
British army, maybe. US Army training was wrong. Marksmanship on the range was not snap shots at fleeting targets or cover fire for effect. Better sights help, but the right kind of target identification and service with the equipment to hand would have helped the American infantry. OJT is the wrong time to unlearn stateside training mistakes.
As I and other have said - Start rearmament at the same time as Germany you end up with an expeditionary force of between 32 and 55 divisions. All motorised. Now the kit wont be as good, maybe, because a lot of the kit actually used is available but either not confirmed or ordered at scale early.
Simplify down to the basics. Rifle, machine gun, mortar, grenades, uniform and field kit. Train, train, train, train. Practice mock war with the territorials so everyone is on the same script. The kit only has to be good enough. The men have to know its use and they have to be confident that they can do the job. No magic bullets to this. It goes back to Julius Caesar.
The Kiraly is heavier than the SMLE. 4.4kg vs 3.9kg. its 1.049m long vs 1.132m for the SMLE and 3.2kg and ,63m for the sten. ( M1 carbine is 2.9kg and .9m) As most of the firepower comes from the Bren which is issued at a rate of 1 per 12 men in the rifle battalion or 1per 8 men in the rifle section in combat ( but 3 of the 8 fire the Bren and 1 is the section commander one may be a rifle grenadier and early on there may be scoped rifles) and at platoon level you add commander, radio man, Mortar team.) Plus an additional company worth of Bren in the carrier platoon plus more 2'' adding a short range automatic in most circumstances, is pointless.
The Brens work as teams. Might want to train the entire section on how to use the thing. Might want to give section leaders SMGs for local security and close in firepower. I like the ZK383 as COTS or steal the Baretta M39 for pre-war.
Also WW2 ( and WW1) shows the key issue on making small arms is not slightly less complicated its capable of being made by unskilled labour using hammers, or as close to that as possible.
Illustrated with the examples compared in the SMGs that have been proposed as candidates.
SMG are useful for airborne, special forces and when you don't have enough LMG. They are also useful for rear area troops who are doing something else as their main job and don't need to carry a big heavy weapon they can't use properly and just gets in the way. But they do need to carry an effective weapon because of airborne, special forces, sudden breakthrough etc. The reason for the panic is not its utility in front line service but lack of LMG and fear of Parachutists dressed as nuns in 1940.
I respectfully disagree about giving amateurs something as dangerous as SMGs. I prefer men of good judgment.
In terms of utility the Red army famous for SMG everywhere has 86 SMG in the 41 infantry bn but when they reduce the strength during 41 that goes down to 18 ( and the LMG component from 36 to 18.) And they lose. By 44 this has gone up to 165 smg and 54 lmg ( but note the soviets usually have 1/3 - 1/2 the LMG ammo on hand compared to the UK) at which point the brits have more of both.
The SU RA also was more comfortable with red on red. See previous comment about SMGs and Private Fumbles
In 1940 the German infantry has 40 smg per bn given to the platoon and squad leaders whose job is to command not fire. And I suspect then the smarter ones then pass them off to AN Other on the grounds that MP = leader = sniper target.
Downside. That is what corporals are for.
The Lesson of Gallipoli is you can evacuate off a beach using ships boats. But that its really hard to build up supplies in that way. Unless you want to make the assumption that the French army will collapse at the first blow this is not a priority. Hence the 1926 Motor landing craft and 1938 Landing craft mechanised being developed by the British, And used in Norway and Dunkirk - and lost there. With LST and LCT following in 1940 but not being built and fielded in large numbers.
The lesson of Vera Cruz is that you design to the operations or one does not do the operations.
"You need ramps for your prams , and plankboard to walk horses and roll guns onto and off the beach, you misbegotten cretins."
Winfield Scott to the people who criticized his delays in mounting his amphibious assault.