Yugoslav fighters, members of the patriot forces, during training at an Allied camp in Italy on Feb. 29, 1944.

Female German army prisoners being checked in by German-speaking Americans at a German Women's Detention Building in 1945. The women were captured at the front on the 7th U.S. Army sector.

Christian Lebanese women, members of Kataeb Phalangist party, train with weapons on Sept. 9, 1976. The Lebanese civil war erupted a year earlier.

Young women learn how to charge an enemy with rifles and bayonets at their high school in Tokyo, Feb. 18, 1937. Japan trained women and girls for auxiliary army units.

Jewish women in the Palestine Auxiliary Territorial Service of the British Army learn how to use gas masks, Oct. 14, 1942. Many of them were in service on the Egyptian front.

Women help each other with bags at an embarkation port in the U.S. in this Jan. 29, 1943, photo provided by the U.S. Army. They were bound for North Africa with the first detachment of the Women'’s Auxiliary Army Corps to be sent abroad.

Female Italian partisans in Castelluccio, Italy, keep weapons ready as they wait for their turn to patrol with the U.S. 5th Army on Feb. 11, 1944.

Members of the Women's Army Corps pose at Camp Shanks, N.Y., before leaving on Feb. 2, 1945. The women were with the first contingent of the Black American WAC to go overseas for the war effort.

Female members of Egypt's "liberation battalions" train in the desert near Cairo for guerrilla warfare against the British in the Suez Canal zone, Nov. 20, 1951.

A female Cambodian soldier totes a machine gun into combat during an operation across the Mekong River from Phnom Penh in the Prek Tamak area of Cambodia on Aug. 26, 1970. This region was the scene of heavy fighting between Cambodian troops and Viet Cong. The young woman is one of many who served as regular soldiers and medics in the rapidly expanded army .

Female soldiers with AK-47 rifles and bayonets march on the parade grounds at the Women's Military Academy in Tripoli, Libya, on Jan. 18, 1986. At rear is a portrait of of Libyan ruler Moammar Gadhafi.

Female members of the North Korea Worker-Peasant Red Guards undertake air defense training in 1970.

Female members of Egypt's "liberation battalions" train in the desert near Cairo for guerrilla warfare against the British in the Suez Canal zone on Nov. 20, 1951.

Traditions break down fast during times of war, and history is full of examples where women assumed dramatic new roles that never would have been possible in times of peace.

As this photo gallery shows, the pressing demands of World War II led many countries to call on women to bolster their armed forces, in jobs ranging from nurse to front-line soldier.

Hundreds of thousands of American women served in the U.S. military during that war, and U.S. women were allowed to fly military aircraft for the first time. Some countries desperate for fighters, like the Soviet Union, put women in combat roles.

When wars end, old rules can often return. The U.S. Congress mandated in 1948 that women should be limited to 2 percent of the force. Women have managed to steadily expand their role in the military since then, and they now make up 15 percent of the military.

But they were barred from combat positions until Defense Secretary Leon Panetta announced Thursday that he was ending that policy.

The U.S. has plenty of examples to learn from. Many European countries, along with Canada and Israel, have permitted women in combat roles for years, citing gender equality. Some Communist countries have also turned to female soldiers for reasons of ideology or propaganda.

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