Women in the military
History: 

World War I: 

United States: During the First World War, women in the United States joined organizations such as the Committee on Public Information to educate people about the war. This committee also promoted nationalism. Many women became YWCA members and went overseas to help soldiers. Women of all classes contributed to the war effort. Upper-class women founded many voluntary war organizations while middle and lower-class women worked in these organizations as nurses or by filling in open positions left by those who had gone to war.

Russia: Russia is the only nation to deploy female combat troops in substantial numbers. Historically, female recruits either joined the military in disguise or were tacitly accepted by their units. Perhaps the most prominent was a contingent of front-line light cavalry in a Cossack regiment commanded from 1915 to 1917 by a female colonel, Alexandra Kudasheva (1873–1921?). This cavalry regiment fought in WWI and also during the Russian Revolution. and may have been the first gender-integrated regiment in Russian history. She was also noted for her endurance riding feats.
Others included Maria Bochkareva, who was decorated three times and promoted to senior NCO rank, while The New York Times reported that a group of twelve schoolgirls from Moscow had enlisted together disguised as young men. In 1917, the Provisional Government raised a number of "Women's Battalions", with Maria Bochkareva given an officer's commission in command. They were disbanded before the end of the year. In the later Russian Civil War, they fought both for the Bolsheviks (infantry) and the White Guard.

Others: In Serbia, some women played key military roles. Scottish doctor Elsie Ingles coordinated a retreat of approximately 8,000 Serbian troops through Romania and revolutionary Russia, up to Scandinavia, and finally onto transport ships back to England. Milunka Savić enlisted in the Serbian army in place of her brother. She fought throughout the war, becoming one of the most decorated women in military history.
In 1917, Loretta Walsh became the first woman in the United States to enlist openly as a woman.  In the 1918 Finnish Civil War, more than 2,000 women fought in the Women's Red Guards.

Spanish Civil War: During the Spanish Civil War, thousands of women fought in mixed-gender combat and rearguard units, or as part of militias.

Second Sino-Japanese War: Several women's battalions were established in China during the Second Sino-Japanese War. These included the Guangxi Women's Battalion, the Yunnan Women's Battlefield Service Unit, Zhejiang Women's Guerrilla Band, Hunan War Service Corps, and others.

World War II: All the major participating nations in World War II enlisted women. The majority served in nursing and clerical or support roles. Over 500,000 women had combat roles in anti-aircraft units in Britain and Germany, as well as front-line units in the Soviet Union.
United States
During World War II in 1941, there was a total of 350,000 women who served in the United States Armed Forces. Women weren't thought to be qualified during these times, however due to the situation the United States decided to have women work in factories making items like aircraft, weapons, and submarines, although for lower pay than men.

India: In 1942, the Indian National Army (Azaad Hind Fauj) established Rani of Jhansi Regiment, India's first all-women regiment to fight for Indian independence under the leadership of Subash Chandra Bose, with Japanese assistance. It is estimated that over 1,000 women served in the regiment.

United Kingdom: In 1938, the British established uniformed services for women (small units of nurses had long been in service). In late 1941, Britain began conscripting women, sending most into factories and some into the military, especially the Auxiliary Territorial Service (ATS) attached to the army. The ATS began as a women's auxiliary in 1938. In 1941, the ATS was granted military status, although women received only two-thirds of male pay. Women had a well-publicized role in handling anti-aircraft guns against German planes and V-1 missiles. Prime Minister Winston Churchill's daughter was there, and he said that any general who saved him 40,000 fighting men had gained the equivalent of a victory. By August 1941, women were operating fire-control instruments; although they were never allowed to pull the trigger, since killing the enemy was considered too masculine. By 1943, 56,000 women were in Anti-Aircraft Command, mostly in units close to London where they faced a risk of death, but not of capture. The first death of a woman in Anti-Aircraft Command occurred in April 1942.

Germany: The Third Reich had similar roles for women. The SS-Helferinnen were regarded as part of the SS if they had undergone training at a Reichsschule SS. All other female workers were contracted to the SS and chosen largely from concentration camps. Women served in auxiliary units in the navy (Kriegshelferinnen), air force (Luftnachrichtenhelferinnen) and army (Nachrichtenhelferin).

In 1944-45 roughly 500,000 women were volunteer uniformed auxiliaries in the German armed forces (Wehrmacht). Approximately the same number served in civil aerial defense. 400,000 volunteered as nurses and many more replaced drafted men in the wartime economy. In the Luftwaffe, women served in combat roles helping to operate anti-aircraft systems to shoot down Allied bombers. By 1945, German women held 85% of the billets as clerics, accountants, interpreters, laboratory workers and administrative workers, together with half of the clerical and junior administrative posts in high-level field headquarters.
The German nursing service consisted of four main organizations: one for Catholics, one for Protestants, the secular DRK (Red Cross), and the "Brown Nurses" for committed Nazi women. Military nursing was primarily handled by the DRK, which came under partial Nazi control. Front line medical services were provided by male medics and doctors. Red Cross nurses served widely within the military medical services, staffing the hospitals close to the front lines and at risk of attack. Two dozen nurses were awarded the Iron Cross for heroism under fire. Brown Nurses were forced to look away while their incapacitated patients were murdered by war criminals.
Hundreds of women auxiliaries (Aufseherin) served in the SS in the camps, the majority of which were at Ravensbrück.
In Germany, women worked and were told by Hitler to produce more pure Aryan children to fight in future wars.
Women also fought in the Volkssturm near the end of World War Two. Girls as young as 14 years were trained in the use of small arms, panzerfaust, machine guns, and hand grenades from December 1944 through May 1945.

Japanese American Women: During the Second World War, many Japanese American women lost their jobs or pay because they were sent to relocation camps. Japanese immigrants and Japanese Americans were faced with discrimination. Many Americans called it the "yellow peril" and called Japanese people "japs".  In 1913, California passed the Alien Land Law which prohibited "aliens ineligible for citizenship" from owning land to grow crops on. Despite the discrimination, many Japanese American women volunteered to serve in the Women's Auxiliary Army Corps. Sexism along with racism was something that these women faced when they joined WAAC. Even while dealing with discrimination, Japanese American women were able to greatly help the United States. Many women were hired as interpreters, translators, and interrogators in the Military Intelligence Service. In 1948, the Women's Army Corps was permanently established and remained until 1978 when women were allowed into the army.

Italy: In Italy, during the second world war, the Female Auxiliary Service (Italian: Servizio Ausiliario Femminile, SAF) was a women's corps of the armed forces of the Italian Social Republic, whose components, all voluntary, were commonly referred to as auxiliaries. The commander was the Brig. Gen. Piera Gatteschi Fondelli.

Yugoslav Partisans: The Yugoslav National Liberation Movement had 6,000,000 civilian supporters; its two million women formed the Antifascist Front of Women (AFŽ), in which the revolutionary coexisted with the traditional. The AFŽ managed schools, hospitals and local governments. About 100,000 women served with 600,000 men in Tito's Yugoslav National Liberation Army. It stressed its dedication to women's rights and gender equality and used the imagery of folklore heroines to attract and legitimize the fighters. After the war, although women were relegated to traditional gender roles, Yugoslavia's historians emphasized women's roles in the resistance. After Yugoslavia broke up in the 1990s, women's contributions to the resistance were forgotten.

Jewish Parachutists of Mandate Palestine: The Jewish Parachutists of Mandate Palestine were a group of 250 Jewish men and women from the Yishuv communities in Mandatory Palestine. The group members would go to missions run by British organisations MI9 and the Special Operations Executive (SOE) involving parachuting into German-occupied Europe.