WW2 gives the earliest examples that I can think of, of section and platoon level tactics that are more or less the same as how we still do it now. Modern Infantry Soldiers and Marines are trained to do the job "1 up", ie if our immediate commander is killed, we can take over and do his job. We are trained on multiple weapon systems, comms, language, low level tactics, and physical fitness to a high level. Given how similar WW2 tactics were, was the training to a similar level or were soldiers trained to a basic level and thrown into combat? I'm wondering about American, British and German forces mostly as I sort of assume Soviet soldiers got very little formal training (happy to be corrected though).
Your premise that modern day infantry tactics originated with World War Two is not entirely correct. Tactics certainly evolved during the interwar era and WWII itself, but this was the continuation of processes that had been ongoing for a very long time. A good example of this is the development of infantry tactics during the Great War. During trench assaults on the western front, British, French and German commanders all found that communication breakdowns (as troops moved across no man’s land, soldiers became isolated, officers became casualties, or communication lines were disrupted by enemy activity) were common, and seriously impacted the efficiency with which a mission could be carried out. They devised numerous workarounds to this problem, including a greater level of emphasis on individual understanding of objectives and tasks, so that each soldier should understand the overall mission, and his role in it. Throughout the war, officers on all levels worked extensively on post-battle analysis, striving to improve tactics so as to give their units and armies an edge over their opponents. A prime example of this on the British side is field manual SS 143 (issued in February 1917, and incorporating lessons learnt during operations in 1915 and 16). It is often held forth as a symbol of the shifting emphasis from large scale manoeuvre to small unit and individual tactics. It introduced the concept of an infantry platoon consisting of independent, but mutually supporting sections and teams, which should move across the battlefield using fire-and-manoeuvre – dealing with or bypassing problems as they were encountered – and it described the training which should prepare the individual rifleman for this type of operation in great detail.
Yet although infantry tactics did indeed evolve extensively during the Great War, it is still a mistake to think of it as the beginning of this process. Training and drill manuals from as far back as the 1700s emphasise individual initiative, as well as fire and movement for light infantry or ranger units – often to a degree which bears striking resemblance to how modern infantry move across the battlefield. If the tactical developments of the Great War symbolises anything, it is rather that this type of small scale operations emphasising individual initiative should be implemented across the army as a whole, rather than be restricted to specialist units. It is also the perfection of the “all-arms” or “combined” operations, where branches of the army should all support each other throughout the battle, rather than operate as individual units. These developments were all prompted by the exponential growth in firepower available to the individual soldier. Until the Franco-German war of 1870-71 soldiers dying from sickness had outnumbered those dying in combat by a factor of 5. By 1918, those numbers had been reversed. As firepower became the means by which military success was achieved, maximising the firepower of individual soldiers, while minimising the effectiveness of the enemy’s, became the goal of military training. The evolution of tactics during the Great War thus emphasised both individuality and cooperation. There were incremental improvements in weaponry and technical equipment through the interwar era, World War II and beyond, but the essential task that an individual soldier was expected to performed changed little, if at all. In this sense, the way western armies operated (and the way in which individual soldiers were trained) in 1918 differed relatively little from how they operated in 1940 or 1945 – or even today.