B6, key topic 1 - Warfare in 1919–39

Industrial War Legacy

In 1919, the most important recent lesson was that war had become industrial. The First World War had involved mass armies, railways, factories, heavy guns, machine guns, chemical weapons, tanks, aircraft and submarines. This did not mean every later conflict looked exactly like the Western Front. It meant that commanders after 1919 had to think about how industry, machines and science changed what was possible.

The First World War had shown two uncomfortable truths. First, firepower could make open movement extremely dangerous. Heavy artillery, machine guns and barbed wire helped create defensive deadlock. Second, new technology could widen the battlefield. Submarines threatened shipping far from land. Aircraft could observe, fight, bomb and attack people who were not in the front line.

Interwar warfare was therefore not a clean break with 1914-18. It was a period of testing. Some armies tried to work out how tanks, aircraft and radios might restore movement. Some governments feared that future war would involve bombing cities. Chemical weapons were restricted by international agreement, but they were still stockpiled and, in Abyssinia, used. The period 1919-39 matters because it shows weapons moving from wartime novelty to planned military method.

A good way to remember the period is: the First World War provided the warning; interwar conflicts provided the testing ground.

Misconception check: "modern warfare" did not mean soldiers stopped fighting on foot. The change was that soldiers increasingly fought inside systems of artillery, aircraft, vehicles, supply lines and communications.

Gas, Tanks And Heavy Artillery

Heavy artillery remained central to land warfare. In the First World War, guns had caused enormous casualties, destroyed trenches, cut wire, smashed roads and railways, and forced soldiers to dig in. By 1919, no serious army could ignore artillery. It was not just a support weapon; it shaped the battlefield before infantry moved.

Gas showed a different kind of change. Poison gas had been introduced during the First World War to break trench deadlock and terrify defenders. It could kill, blind, burn lungs and skin, and force soldiers to wear awkward protective equipment. Gas did not become the decisive war-winning weapon some people expected, partly because defences improved, but its psychological effect was huge. The fear of gas became part of interwar military and civilian planning.

Tanks were an answer to the problem of movement. They were designed to cross shell holes and wire while giving troops protected firepower. Early tanks were slow and unreliable, but they suggested a future in which armour could help break through defensive lines. By the late 1930s, the key question was not simply "Who has tanks?" It was "Can tanks be used with infantry, artillery, aircraft, fuel, maintenance and communications?"

The important change was combination. A tank alone was not enough. A bomber alone was not enough. A shell alone was not enough. Modern warfare increasingly depended on coordinating different weapons so that firepower, movement and shock reinforced each other.

Submarines And Sea War

The emergence of submarines changed sea warfare because they made invisibility a weapon. Before the twentieth century, naval power was usually imagined through battleships, cruisers, blockades and surface fleets. Submarines added a new danger: a vessel could attack from beneath the surface, threatening warships, merchant shipping and supply routes.

The First World War made this clear. German U-boats attacked Allied and neutral shipping, and unrestricted submarine warfare caused major political anger because civilian ships and neutral trade could be drawn into war. This mattered after 1919 because governments understood that a future war would not only be fought by armies at the front. It could also be fought against imports, food, fuel and the merchant ships that kept a country alive.

Submarines did not replace surface fleets. Battleships, cruisers, aircraft carriers and destroyers still mattered. In fact, submarines created new demands for anti-submarine warfare: convoys, patrol aircraft, depth charges, escorts and intelligence. The change was that naval warfare became more hidden and more directly connected to civilian survival.

This is especially important for a breadth-study answer. Submarines show change in method rather than just change in weapon. Sea power was no longer only about defeating an enemy fleet in battle. It could mean wearing down an enemy economy by attacking supply lines.

Misconception check: submarines were not "new" in 1939, but their military importance had emerged in modern form by the First World War and shaped planning before the Second World War.

Air Power In East Asia

Air power became a visible part of conflict in East Asia during the 1930s. Japan expanded its control in Manchuria from 1931 and full-scale war with China began in 1937. The official key topic does not require the whole Second Sino-Japanese War, but it does require the use of fighter and bomber aircraft in East Asia.

Fighter aircraft mattered because armies needed control of the air. Fighters could intercept bombers, protect their own aircraft and attack enemy planes. Bomber aircraft mattered because they could attack beyond the immediate front: airfields, railways, ports, troop concentrations and cities. This made the battlefield deeper. A railway junction, factory district or crowded city street could become part of the war.

In 1937, Shanghai and Nanjing showed the importance and danger of air warfare. Fighting in and around Shanghai involved urban combat, naval power, aircraft and bombing. Around Nanjing, aerial battle and bombing formed part of Japan's advance. Japan's air superiority helped it attack Chinese cities and weaken Chinese resistance, although air power did not win the war by itself. Armies, supply lines, sea control and political endurance still mattered.

East Asia therefore shows two changes at once: