Men only. No women
In the U.S., the Selective Service, (the U.S. draft for military service) has always mandated that only men may be drafted into military service.
2 men, with the backing of several civil rights groups have challenged that law, claiming that it is discrimination against men. The selective service mandates that on his 18th birthday every male MUST report and register for the draft. This is the only remaining gender based Federal law.
The law has been challenged in The Supreme Court of the United States. Unfortunately, the Supreme Court has refused to look at this discriminatory law claiming that it is up to Congress and not the Judiciary.
I say 'unfortunately' because women have demanded equal protection under the law. In my opinion, women can not, will not, ever achieve equality unless they also bear equal responsibility.
Note: it is not absolutely necessary for women to actually be in ground combat. However, some women do make it into combat provided they have volunteered; example pilots. There are thousands of other military jobs that women are able to do besides combat.
The main point I make is that when women are REQUIRED to have their lives disrupted and forced into positions they wound not otherwise choose, only then will they bear full responsibility.