The logic is flawed unless the younger brother enlisted in an elite unit. Once you sign up, the army will send you wherever they need you. You can make a request but it’s not likely to make much of a difference. However, if the brother was able to get accepted into a specialised unit then the older brother has more of a chance to end up on the same base if he too is accepted.

Otherwise, it’s not clear to me how he plans on getting his brother out of service. If his goal is to get his little bro out, him simply being a soldier ain’t going to do it.

In Hair, for example, Burger planned on taking Bukowski’s place for an afternoon as a means of giving him a day off. The logic there was that the commanding officers couldn’t tell the difference between them once in uniform. That’s a minor problem when the unit gets called up to Vietnam and it could be argued that the sergeants sent to ship the men out weren’t familiar with the troops so the logic still works.