Britain, again faced with demands that women be allowed to join combat units, ran tests with volunteers to see if women could meet the demands of ground combat. One test required the volunteers to carry 90 pounds of ammunition over a measured distance. In combat, this is a common chore, bringing ammo and other supplies up to front line units that cannot be reached by vehicles (because of enemy fire and/or terrain.) Eighty percent of the men were able to accomplish this chore, but only 30 percent of the women. Another test involved making a 20 kilometer march, followed by a live firing exercise (to simulate the combat that would often follow such a march.) Everyone carried sixty pounds of weapons and equipment. For the men, 83 percent were successful, for the women, only 52 percent were. Many other tests were "gender normed" (lower standards for women), and still the men out performed the women. This is hardly the first time an attempt has been made to put women in ground combat units. Since the development of lightweight firearms about a century ago, it suddenly became  possible for women to handle their weapons as effectively as the men. Before that, the weapons depended too much on upper body strength, leaving women at a large disadvantage. But attempts at using women as infantry have nearly all failed. Some of the reasons have to do with the muscle issue. But there are others as well. Women are more prone to bone and muscle injuries than men. This is now being rediscovered as more adolescent females engage in vigorous sports like basketball and soccer. They have much higher injury rates than the boys. There is also the psychological angle; men tend to be more enthusiastic, or at least less freaked out, when it comes to killing. However, there have been instances when women have been successful as infantry, at least irregular light infantry (guerillas.) The partisan war in Russia and the Balkans during World War II saw thousands of women toting guns and fighting alongside the men. This was due to a severe shortage of fighters. You took whatever you could get, including teenagers. But guerillas don't fight like regular infantry. They spend most of their time avoiding the enemy. When they do fight, they travel light, as "hit and run" is their most successful from of combat. A woman can set up an ambush, fire off her weapon and then scamper away into the bush as well as a man. The Tamil rebels in Sri Lanka use a lot of women as guerilla fighters. But, recognizing the physical and psychological problems, the women are usually used in fortified positions (it's easier mentally to be under cover and fire at the enemy and you don't have to worry about how much you can carry or whether you'll pull a muscle or throw you knee out.) The Eritrean army used thousands of women in its wars against neighboring Ethiopia, mainly because Ethiopia had population fifteen times that of Eritrea. But the women were used mainly in fixed positions. Another problem, pregnancy, was largely solved by the food shortage. Most women, if their body fat falls below a certain level, cannot conceive. Such was not the case among the European World War II guerillas. The Balkan guerillas solved the problem by declaring unauthorized pregnancy a capital offence. Before the woman was executed, she was asked to identify the father. She could tag some guy she didn't like rather than the real daddy. This was great for morale. In any event, many of the Balkan female guerillas hooked up with one guerilla leader or another and became a "field wife" for the duration of the war. Most nations that have put women into combat units in the last century have reversed that decision once the fighting got going. It just didn't work. There were exceptions, like the female guerillas and women snipers in the Russian army, but by and large the problems were not worth the benefits.