The readiness of our armed forces is a serious matter.  Transgenders serving along side others in some cases would be no problem, but frankly, I don't want a transgendered women to man in the fox hole next to me when my life is at stake.
I don't want the military and it's budget used to pay for the operations to change a person sex and then pay for the recovery time it takes to be back to fighting shape.
We do have a volunteer military now and choices are made for type of job available for many of these individuals, but in a time of war (and that is what we must alway be prepared for) the people that might be sitting at a desk, may be called to the front lines in some area.  They need to be prepared and effective in holding their own.  Besides, it might be unconfortable for them is their uniform colors would clash.