Its beneficiaries are active duty military, retired military, and dependents of same, although the access for these last groups are somewhat restricted.
The military system has its own hospitals and clinics. The doctors and nurses in this system are mostly active duty military officers (I was one of them for most of my career), with the money sometimes paying for civilian "contract" doctors and nurses if there is a shortage of active duty to take care of something.
Military veterans also have a large federally funded health care system, the VA, also with its own salaried federal doctors etc. This is for people who may not qualify as "retired" for care under the military system, but have service related disability or illness that require ongoing care. Let's say you acquired hepatitis from a blood transfusion while active duty ("line of duty"). When you get out of the military, you are still healthy but carry the virus. Subsequently you develop liver problems from ongoing hepatitis requiring care... you should be eligible for care under the VA system.
People who work for federal government agencies like NASA etc. do NOT get this kind of socialized care but get insurance benefits through their work for care like most other people.
Both the military and VA systems are "socialized medicine", i.e. government provided care with salaried providers who have no profit incentive.
I felt the care delivered via the military's socialized medical system was good, of course I'm biased since I spent most of my career delivering it. I make a lot more money in the private sector. There are definite advantages to the private system, but there are also advantages to the socialized system.
Socialized system:
Advantages:
-Everyone (in the system) is covered
-No "profit motive" to do unnecessary procedures
-No "cost cutting" motive to ELIMINATE necessary procedures/medicines
Disadvantages:
-Because of no profit motive, more wait for elective procedures (private sector would whip up more capacity to MAKE THAT MONEY)
-Best doctors tend to leave the system due to lots more $$ in private sector (there are many notable exceptions to this, and I've certainly known many, many superior doctors who spent a full career in the military, and known some real stiffs in the private world).
Private system:
Advantages:
-Many excellent doctors to be found there due to high reimbursement
-Easier access to things like surgical procedures, profit motive spurs doctors and hospitals to create access to these
Disadvantages:
-Profit provides incentive for unnecessary surgery/procedures
-Lack of access for those without jobs/insurance
-Tiered system where many of the most prestigious doctors don't want to care for those with no insurance or lower paying insurance like Medicare/Medicaid
-Cost cutting motive (as in HMOs) provides incentive to ELIMINATE possibly needed or beneficial procedures/surgery/medication
These advantages/disadvantages are just a few things right off the top of my head...