As with most Japanese military doctrinal measures, it differed based off of what branch the infantry were in as well as the purpose of the infantry in question.

Unlike American forces which usually had a plethora of support weapons integrated both within their direct units as well as designated supporting forces, Japanese forces typically lacked the higher firepower options due to weak industrial strength. To compare, a 1944 US infantry division would have 66 howitzers, 57 anti-tank guns, 144 mortars, and a plethora of anti-tank launchers, heavy machine guns, and other supporting equipment. A Japanese 1944 infantry division on the other hand had around 150 grenade dispensers (the so-called "knee mortar"), 66 howitzers, 18 anti-tank guns, LMG-equipped squads and LMG/HMG-equipped support squads. They sound not too different, until you realize that the American artillery was significantly better than the Japanese artillery, and that a Japanese division consisted of 20,000 men while the US division contained 14,000. In effect, from a sheer quantity point of view, the Japanese were outgunned 1.5:1. From a quality point of view, the Japanese were outgunned 3:1.

In addition, the Japanese lacked the mechanization that US infantry divisions benefited from, and were heavily reliant on pack animals. A US division could call on over a thousand support vehicles for its logistical needs, while the Japanese were lucky to have barely over 100, to say nothing of superior American build quality and machines.

The Japanese were not ignorant of these industrial and logistical differences, stupid as the decision to go to war may have been. Thus Japanese infantry doctrine sought to maximize their advantage of having less equipment-which is to say, to take advantage of a more mobile infantry force-while minimizing the superior firepower of an American force. Thus the Japanese adapted what were essentially light infantry tactics, which I talk about a bit here.

Of course, Japanese troops played different roles in different theaters. Some Japanese troops were deployed in the static defense role, essentially "Fortress" troops, where they hoped their static defensive works and fortifications would nullify the Allied firepower advantage. Japanese naval troops were an entirely different beast, being equipped with more heavy weapons as these "Special Naval Landing Forces" were expected to be autonomous and were controlled by the Imperial Japanese Navy, not the Army. Units in China were more likely to have tank support as it was more logistically feasible: units fighting in say Guadalcanal were lucky to be able to bring more than their rifles and light machine guns.

All-in-all, the Japanese doctrine focused less on a particular set of tactics than it did on an overall recognition of logistical and organizational needs. They were willing to create ad hoc and temporary organizational units for a variety of tactical and operational needs as necessary, although paper shuffling can only go so far in equalizing against a larger number of tanks and guns.

There is one more note to add to this discussion that did not seem to fit under any of the other responses. It is important to recognize that French and British infantry doctrine was a product of the First World War more profoundly and persistently than any of the other combatants, and this produced facets of those doctrines that are odd in comparison to the rest.

By the end of 1918, the British Army was widely considered the best practitioner of combined arms warfare on the Western Front. Part of the reason for this was the careful use of artillery, aircraft, massed machine guns, and tanks together with infantry. But another vital component of this was having tightly defined objectives, routes, and schedules for advance. This tight control was critical in trench warfare, as combat had a tendency to deteriorate into constant counterattacks sweeping back and forth across the front until they broke at the maximum range of their supporting artillery. Artillery coordination was the single most difficult and important part of an advance, as radios were not portable in that era, and this meant that detailed barrage schedules and carefully organized signals to the front had to be planned out in advance. Another key British innovation was to keep advances short and focused enough that inevitable German counterattacks would smash into a well organized brick wall. The French also adopted, adapted, or independently pioneered most of these methods as well, leading to the tremendous French achievements of the Hundred Days Offensive.

The brevity of the span between the World Wars is often forgotten, but it is important to understand that in 1939 WW1 was more recent than the First Gulf War or the NATO intervention in Bosnia are today. Almost all of the cohort of officers who came to middle and senior positions of authority during this time were veterans of that final glorious offensive in France and Belgium and had internalized its lessons. This produced a command structure built on detailed and careful communication, short tightly controlled movements, and heavy reliance on infantry-artillery coordination. (It is important to note that artillery was easily the most lethal type of weapon in WW1 and, together with mortars, WW2 as well.) Infantry doctrine was also built in a trench sensibility, so that infantry sections were built around the Bren Gun which was capable of walking fire; a popular WW1 concept involving not-too-accurate but voluminously automatic weapons laying suppressing fire while advancing, usually firing from the gunners hip. Similarly, belt fed weapons were not integrated at the small unit level, but instead concentrated in special companies in each battalion. (Later this became platoons in each company.) This was built on the belief that belt-fed weapons should not be expected to move with an assault, but instead lay suppression in pre-planned massed fusillades as had been done in the trenches. Similarly, the British relied throughout the war on the two-inch mortar as their integrated small unit support mortar. This weapon was not powerful enough to be very effective firing explosives (which is why the Germans quickly abandoned a similar weapon when they found it was ineffective on the Eastern Front). But British doctrine assumed that infantry would only advancing with strong artillery support, so the mortar was intended primarily to fire smoke to protect the advance.

While British and French tactical thinking changed little in the 21 years between the World War, one thing that did change enormously was how the army and especially infantry officers were viewed by the public in those countries. As there grew up the "lions led by donkeys" and Colonel Blimp narratives about the deep stupidity and callousness of infantry officers, commanders faced an additional moral pressure to reduce wastefulness and reckless risks of their soldiers' lives. Combined with the military lessons about careful planning from the trenches, this produced a culture of discouraging initiative at the junior officer level. Everyone was given very detailed orders, and expected to carry them out exactly without deviation. It also produced a culture of senior officers feeling they had to prove that they were intelligent, verging on all-knowing. (This is part of the reason why Montgomery's famous "grip" that he asserted from his arrival in North Africa proved so positive to British morale. Monty projected clearly that had a plan, he knew his business, and everyone was expected to do their part, and the soldiers found this enormously encouraging.) This clash of cultures was brought forward when the British started working closely with the Americans, who had a slightly different "social contract" inside the armed services.^(1)

All of these biases faced a rude awakening in May of 1940 when the Germans at last launched their assault on France and the Low Countries. Not to stray too far away from the smaller-unit level, but there were enormous difficulties adapting to the tempo of operations at every level of command. The French, who are treated enormously unfairly by popular history, had a very solid doctrine for waging the battles of 1914 over again, but their communication below the division-level relied on telephones and miles of wire that could not be moved quickly. Junior and lower grade field officers were reluctant to order counterattacks on their own authority, and senior command was slow to pass on instructions. Attacks that could have changed the history at dusk were delayed until they were irrelevant in the morning. The British, who had prepared more conscientiously for mobile warfare and had far more resilient communication systems, also proved unsteady at adapting to the speed and scale of these operations. (One little noted example of how well Britain had prepared for aspects of mobile warfare was Operation Compass, in which they used the speed of their armored columns to annihilate an Italian Army.)

In the wake of the trauma of Dunkirk, the British Army began to adapt, but most of the salient lessons of France had little to do with infantry tactics. The main focus during this time period was developing the use of armor, air-support, and mechanization in about that order. In addition, Britain's main incubator of ideas shifted to North Africa (though there were some important lessons about prompt infantry counterattacks ordered by field-grade officers that could have been learned from Crete if anyone had bothered to look). North Africa was not an infantryman's theater, due to its topographic idiosyncrasies, despite the famous and vital role played by the infantry in several major engagements. The peculiarities of desert warfare made infantry-armor coordination work differently there than anywhere else, and the windowpane-flat terrain made infantry advances primarily a function of close artillery support. So infantry tactics did not really change much during this interval. It mostly consisted of continuing the careful artillery planning of WW1, and combining it with the speed and versatility of better radio communication and effective air support.

One place where this emphasis on WW1-style planning and objective lines proved a real boon was in Italy, which is probably the theater in which the British infantry performed best. The slow systematic process of mountain warfare was ideally suited to deliberate focused offensives. In France, the British Army substantially improved its infantry-armor coordination but continued to be, as Anthony Beevor has stated, "perpetually slow to reinforce success".^(2) The British Army did not adopt their American ally's innovation of handing fire-mission authority to junior officers and non-coms, they still relied almost exclusively on the under-powered two-inch mortar, and they still lacked a belt-fed automatic weapon that weighed fewer than 50 lbs. It is little noted that, after the war, the British Army experienced an eruption in innovation in designing small arms (as well as armor). But in 1945, this wave of innovation in infantry doctrine was still in the future.

Post Script: the peculiar reliance on objective lines and detailed planning in British operations even applied in armored warfare. One of the best sources I have seen that mentions this, and frankly one of the best military documentaries ever made, was assembled by the British Directorate of Army Training / War College in the 1970's and is simply called Operation Goodwood which interviews several key participants in that battle (including Hans von Luck). It is hard to find in any official way, but I don't think it is under copyright. Here is where one YouTuber has put it up in its entirety. I strongly recommend it to anyone interested topics of military history and doctrine in any way.

Notes:

1. Eisenhower's Armies by Niall Barr (2015)
2. D-Day: The Battle for Normandy by Anthony Beevor (2009)

Follow-on question about the German infantry's LMG-orientation. This was particularly effective when in a defensive posture, such as on the Western front facing the attacking Anglo-American armies. The US Army was so impressed with the MG42 that they basically copied it, slowed down the rate of fire, and called it the M60.

However, this tactic seems less effective when on the offensive. What were the German Army's squad tactics during the offensive (for them) period of the war, from 1939-41?

I can answer this in regards to British doctrine prior to the evacuation at Dunkirk and in particular the expeditionary force that was sent to France. However, as you might expect the involvement of Commonwealth forces, American and other Allied armies after this changed the military role of the British Armed Forces. Britain's role in the war was substantially different from D-Day, compared to it's involvement with attempting to repel Germany's initial invasion of Western Europe.

Likewise I can briefly comment on British doctrine when it came to the Pacific theatre, but this again will be prior to Pearl Harbour and the United States becoming involved in the theatre also.

In regards to the expeditionary force and that of France, British doctrine was relied heavily on support vehicles. The Bren (or universal carrier) would be a staple of this. Troops would readily move into an engagement and subsequently disembark and engage the enemy. This is somewhat different from the examples you have given in your question. This is in large part due to the nature of the role the British expeditionary force was to play. Many of the commanders at the time theorised that this war, like the last would play out exactly the same as World War One. I will have to check my source again, but I believe Churchill was even of the belief that the German Panzer divisions, while broken through French lines, would require support from the infantry of the Wehrmacht. This in turn led to the further assumption that the Panzers that had broken through would not be able to hold any territory that they had gained. Thus, infantry doctrine was similar to that of the First World War. Entrenchment and holding strategic areas with rifle companies and artillery support. In addition to the Bren, the Mark IV was also a light tank dispatched to France during the initial phase of the war. However, as mentioned, British doctrine was very much the same as it had been in the First World War, and thus these tanks acted as a form of 'modern' cavalry. In turn, when these vehicles were overwhelmed by the far superior firepower of the Panzer III and IV, a change in strategy would become necessary for any further engagement with German Panzer Divisions.

In the interim of the war (with France defeated and the USA yet to enter) British infantry doctrine moved to a heavy reliance on Special forces. Small teams of men would be deployed to destory key facilities aiding the german war effort (notably in Norway). The infantry doctrine deployed in these scenarios were drastically different as I am sure you can imagine. These teams relied heavily on their sub machine guns and explosives to inflict as much damage as possible to German forces. This change in doctrine came with the realisation by both British and French command that any attempt to launch a land invasion of mainland Europe would ultimately be fruitless. This acknowledgement is perhaps most commonly noted by Churchills 'Blood toil, tears and Sweat' speech, in which he calls to "the new world". While he mentioned this would be at the liberation of the old, many historians also speculate it was a call to arms to America at that moment in time also.

The Pacific theatre for the British and the commanders of this front also had a substantially different role to play. For the most part, it was common knowledge amongst the upper echelons of British government and the military command that in the event of Britain being tied up in Europe, sufficient relief would not be able to aid Britain's imperial territory in the Pacific. Further reading on this can be found in regard to the Singapore strategy, which relied extensively on the Royal Navy being in a position to aid any aggression from another Imperial power (in this case, the Japanese). The Infantry doctrine was in turn minimal, with most divisions in Malaya, Hong Kong and other Pacific islands being supplied in large part with the Lee Enfield rifle.

As mentioned, I'm afraid I can't go into substantial detail about Commonwealth forces, and how the British Empire acted in the Asian mainland against Imperial Japan, but I hope this can act as a foundation to answer to your question.

Further reading for the Pacific, I would highly recommend Martin Thomas, 'Crisis of Empire'. While the book doesn't directly related to British infantry doctrine, it gives a valuable insight into why Britain was so handily defeated by Imperial Japan.

(Trying to edit a few things here and there, as well as add in any additional information. Not quite there with typing on an Ipad instead of at my PC, apologies).

Follow up question: what was Italian and French doctrine like?

For the uninitiated, can you explain what the acronyms are? LMG and SMG mean nothing to me, but I'm interested in the topic

Late to the party but I (partially) wrote my thesis on this. As previous commentators have noted, Japan's relatively weak industrial base meant that Japanese soldiers couldn't rely on heavy equipment in the same way that their American, British, and eventually Chinese adversaries could, but Japanese infantry doctrine was also heavily influenced by the experience of the 1904-1905 Russo-Japanese War. This was before the advent of mechanized warfare or the military application of much of the technology that was so important to the Second World War, but it was at a time when artillery was becoming more and more crucial to military doctrine. The Japanese military at the time was largely German-trained, and sought to adopt the lessons of the earlier Franco-Prussian War, where superior firepower and technology had secured a quick Prussian victory. Unfortunately, thanks largely to its narrow industrial base, at the outbreak of war, the Japanese army suffered from an acute shortage of shells. The natural result was that Japanese artillery was ineffective at dislodging Russian resistance, and strategic positions often had to be taken by massed infantry assaults, the predecessors to the latter day "bansai attacks." Now these assaults produced high casualties, but they also produced concrete results, largely due to the fact that the Russians suffered from a chronic lack of morale and were themselves badly supplied.

After Japan's stunning victory, the Japanese high command struggled to agree on what the lessons of the war were. Two opposing factions quickly formed. One faction, led by Army Chief of Staff Kodama Gentaro argued that while victory had been achieved, the costs of that victory were unacceptable, and that the country needed to focus on expanding its production base and technological capabilities to avoid a possible future bloodbath. Standing in opposition was a faction led by Maj. General Nagaoka Gaishi, which was heavily influenced by contemporary interpretations of bushido, or the supposed Feudal Japanese "way of the warrior." In the racial determinism of the early 20th century, this faction argued that the Japanese race had a natural tendency towards martial prowess, and that Japanese victory had come from the innate "spiritual strength" of the Japanese fighting man. While Kodama recoiled from the mass casualties of the war, Nagaoka and his followers saw it as a sign of strength, arguing that the fact that Japanese men were so willing to lay down their lives for the country proved that Japan simply had to further unleash the supposedly innate martiality of their men. These officials argued for a harsh regime of indoctrination and discipline in order to secure victory in the future. Due in no small part to Japan's meager industrial base, Nagaoka and his faction eventually won out, with "spiritual strength" and "human bullets" forming the backbone of Japanese military doctrine. The Japanese military placed inhuman expectations on its men. In 1908, allowing oneself to be captured by the enemy became a capital offense, and a 1909 overhaul of official military doctrine cemented the bayonet charge as the fundamental tactic of Japanese infantry. Some historians have argued that Japan's scanty participation in the carnage of the First World War led to this doctrine's survival, long after similar ideas had become obsolete in the other major armies of the time. Tragically, the idea of "human bullets" was indoctrinated into Japanese men from a very young age. One infamous lesson from an early 20th century school textbook featured a supposed anecdote from the First Sino-Japanese War in which an officer finds a sailor weeping over a letter from home. Assuming the sailor is crying tears of emotion, having received a love letter from his sweetheart, the officer admonishes the soldier. However, the officer is surprised and pleased when the sailor explains that he is actually crying tears of shame, as his mother had written to him, expressing disappointment that he had not died in battle like an honorable Japanese man.

This Japanese military doctrine was steeped in ideas of Japanese racial supremacy, invariably contributing to many of the grievous war crimes that Japanese soldiers would commit across China and the Pacific. It also led to the pointless deaths of hundreds of thousands of Japanese men and boys, as commanders ordered bayonet charge after bayonet charge through 1945. Nohara Teishin, a Japanese soldier, recalls one instance in China: "At a terrible place we called Susaku Seitaku, we had our toughest fight. The enemy was behind cover, shooting at us through loopholes in walls, so our dead just piled up…soldiers were expended like this." These attacks often confounded Allied soldiers. Marine Eugene Sledge recalled: "Their effort was admirable but so hopeless…The Japanese held their rifles at port arms and didn’t even fire at us. Everybody along our line was yelling and firing…Within seconds, eight of the ten enemy soldiers pitched forward, spun around, or slumped to the deck, dead where they fell."

If you're interested in this topic, check out Oleg Benesch's Inventing the Way of the Samurai and Harry Wray's The Lesson of the Textbooks. If you like primary sources, Richard J. Aldridge's The Faraway War is an excellent compilation of first hand accounts from both sides of the War in the Pacific.

Follow up: did the use of the M1 Garand influence the US infantry doctrine of prioritizing rifleman as the rate of fire was substantially higher than the bolt-actions fielded by most other nations?

It's worth adding to previous replies about the British that, much like the Germans, the British infantrymen's job often seemed to be to carry ammunition for the section LMG (Buckley [2013], 134-5). The British Bren was a more accurate and portable, and less ammunition-hungry weapon than the German machine-guns, so it was more practical in the assault; but in effect both armies deployed sections based around the LMG which provided most of its firepower.

British infantry doctrine went further than this though. Arguably the British Army didn't have much of a doctrine at all; it was believed that commanders on the ground needed freedom to make decisions without being fed the 'right' solution according to the doctrine (this is superficially similar to 'auftragstaktik' in the German Army, but there all operated according to common procedures which meant teamwork was easy and predictable in the absence of higher direction; the British had nothing of the sort) (French [2000], 21-2). When Montgomery insisted that in 1944-5 all arms would play their part as dictated in his master plan, this was a step forward in doctrine (I don't agree with /u/Prosodism that this was a continuation of WWI methods). As Timothy Harrison Place has argued, there was a dichotomy in British infantry technique between highly orchestrated attacks where infantry minor tactics were of minor importance compared to the artillery fireplan which neutralised the enemy and 'walked' the attacking troops forwards, and engagements where the infantry had to overcome the enemy using their own tactics and resources (Place [2000], 67-8, 76).

The criticism directed at the British infantry often fails to account for the constraining effect of operating according to a larger plan, as well as the fact that when the infantry had to confront the enemy alone this was usually because their support had failed and they were left to attempt objectives which had quite rightly never been assigned to unsupported infantry in the first place. Arguably the infantry was quite capable tactically, but simply didn't have much opportunity to demonstrate this. Anecdotal evidence abounds that British soldiers thought the Germans too static, too reliant on their machine guns (Allport [2015], 232), nervous and unsure at night, and too reluctant to patrol. Sidney Jary believed his platoon were 'better soldiers than any we fought' (Jary [1987], 16). Buckley (2013, 4-18) provides a good explanation for the political and historiographical reasons that the performance of the British Army has, he believes, been unfairly maligned.

Sources: Alan Allport, Browned Off and Bloody Minded: The British Soldier Goes to War, 1939-1945 (Yale, 2015); John Buckley, Monty's Men: The British Army and the Liberation of Europe (Yale, 2013); David French, Raising Churchill's Army (Oxford, 2000); Timothy Harrison Place, Military Training in the British Army, 1940-1944 (London, 2000); Sidney Jary, 18 Platoon (Winchester, 1987).

The OP says that the soviet infantry doctrine "revolved around the SMG" is this correct? I know they had more than was common in other armies, but was this a doctrinal focus?