Military production during World War II was the production or mobilization of arms, ammunition, personnel and financing by the belligerents of the war, from the occupation of Austria in early 1938 to the surrender and occupation of Japan in late 1945.

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The mobilization of funds, people, natural resources and material for the production and supply of military equipment and military forces during World War II was a critical component of the war effort. During the conflict, the Allies outpaced the Axis powers in most production categories. Access to the funding and industrial resources necessary to sustain the war effort was linked to their respective economic and political alliances.

During the 1930s, political forces in Germany increased their financial investment in the military to develop the armed forces required to support near and long-term political and territorial goals. Germany's economic, scientific, research, and industrial capabilities were one of the most technically advanced in the world at the time, supporting a rapidly growing, innovative military. However, access to (and control of) the resources and production capacity required to entertain long-term goals (such as European control, German territorial expansion and the destruction of the USSR) were limited. Political demands necessitated the expansion of Germany's control of natural and human resources, industrial capacity and farmland beyond its borders. Germany's military production was tied to resources outside its area of control, a great disadvantage as compared to the Allies.

In 1938 Britain was the world's superpower, with political and economic control of a quarter of the world's population, industry and resources, and closely allied with the independent Dominion nations (such as Canada and South Africa). From 1938 to mid-1942, the British coordinated the Allied effort in all global theatres. They fought the German, Italian, Japanese and Vichy armies, air forces and navies across Europe, Africa, Asia, the Middle East, India, the Mediterranean and in the Atlantic, Indian, Pacific and Arctic Oceans. British forces destroyed Italian armies in North and East Africa, and occupied or enlisted overseas colonies of occupied European nations. Following engagements with Axis forces, British Empire troops occupied Libya, Italian Somaliland, Eritrea, Ethiopia, Iran and Iraq. The Empire funded and delivered supplies by Arctic convoys to the USSR, and supported Free French forces to recapture French Equatorial Africa. Britain also established governments in exile in London to rally support in occupied Europe for the Allied effort. The British held back or slowed the Axis powers for three years while mobilising their globally integrated economy and industrial infrastructure to build what became, by 1942, the most extensive military apparatus of the war. This allowed their later allies (such as the United States) to mobilise their economies and develop the military forces required to play a role in the war effort, and for the British to go on the offensive in its theatres of operation.

The entry of the United States into the war in late 1941 injected financial, human and industrial resources into Allied operations. The US produced more than its own military forces required and armed itself and its allies for the most industrialized war in history.^[1] At the beginning of the war, the British and French placed large orders for aircraft with American manufacturers and the US Congress approved plans to increase its air forces by 3,000 planes. In May 1940, Franklin D. Roosevelt called for the production of 185,000 aeroplanes, 120,000 tanks, 55,000 anti-aircraft guns and 18 million tons of merchant shipping in two years. Adolf Hitler was told by his advisors that this was American propaganda; in 1939, annual aircraft production for the US military was less than 3,000 planes. By the end of the war US factories had produced 300,000 planes,^[2][3] and by 1944 had produced two-thirds of the Allied military equipment used in the war^{[citation needed]} — bringing military forces into play in North and South America, the Caribbean, the Atlantic, Western Europe and the Pacific.

The U.S. produced vast quantities of military equipment into late 1945, including nuclear weapons, and became the strongest, most technologically advanced military force in the world. In addition to out-producing the Axis, the Allies produced technological innovations; through the Tizard Mission, British contributions included radar (instrumental in winning the Battle of Britain), sonar (improving their ability to sink U-boats), and the proximity fuze; the Americans led the British-originated Manhattan Project (which eliminated the need to invade Japan). The proximity fuze, for example, was five times as effective as contact or timed fuzes and was devastating in naval use against Japanese aircraft and so effective against German ground troops that General George S. Patton said it "won the Battle of the Bulge for us."^[4]

The human and social costs of the war on the population of the USSR were immense, with combat deaths alone in the millions. Recognising the importance of their population and industrial production to the war effort, the USSR evacuated the majority of its European territory—moving 2,500 factories, 17 million people and great quantities of resources to the east.^[5] Out of German reach, the USSR produced equipment and forces critical to their victory in Europe. Over one million women served in the Soviet armed forces.

The statistics below illustrate the extent to which the Allies outproduced the Axis. Production of machine tools tripled, and thousands of ships were built in shipyards which did not exist before the war.^[6] According to William S. Knudsen, "We won because we smothered the enemy in an avalanche of production, the like of which he had never seen, nor dreamed possible."^[7]

Access to resources and to large, controlled international labour pools, and the ability to build arms in relative peace, were critical to the eventual victory of the Allies. Donald Douglas (founder of the Douglas Aircraft Company) declared, "Here's proof that free men can out-produce slaves."^[8]

Gross domestic product (GDP) provides insight into the relative strength of the belligerents in the run up to, and during the conflict.

Romanian, Hungarian, Bulgarian and Albanian GDP calculated by multiplying the GDP per capita of the four countries in 1938 ($1,242 for Romania, $2,655 for Hungary, $1,595 for Bulgaria and over $900 for Albania)^[28] by their estimated populations in 1938: 19,750,000 for Romania,^[29] 9,082,400 for Hungary,^[30] 6,380,000 for Bulgaria^[31] and 1,040,400 for Albania.^[32]

Table notes

1. France to Axis: 1940:50% (light green), 1941–44:100% (brown)
2. USSR to Allies: 1941:44% (light green), 1942–1945:100%.
3. US direct support to the Allies begins with Lend Lease in March 1941, though the US made it possible for the Allies to purchase US-produced materiel from 1939^[33]
4. Italy to Allies and Axis: 1938:0%, 1939–1943:100% Axis (brown), 1944-1945:100% Allies
5. Japanese to Axis begins with Tripartite Pact in 1940
6. The Allied and Axis totals are not the immediate sum of the table values; see the distribution rules^{[clarification needed]} used above.

• Allied technological cooperation during World War II
• Combined Food Board
• Combined Munitions Assignments Board
• Combined Raw Materials Board
• Combined Shipping Adjustment Board
• War Production Board
• American armored fighting vehicle production during World War II
• British armoured fighting vehicle production during World War II
• German armored fighting vehicle production during World War II
• Soviet industry in World War II
  • Soviet armored fighting vehicle production during World War II
• United States aircraft production during World War II
• Forced labour under German rule during World War II
• Technology during World War II