Veterans who are unable to work should apply for Social Security disability benefits. Social Security has an expedited process for veterans who were injured while on active duty after October 1, 2001. You don't have to be injured in battle, just while on active duty. This fact sheet provides additional details.
Many disabled veterans are already receiving benefits from the Veterans Administration. A disability determination by the VA is not binding upon the SSA, because Social Security uses a different disability standard than the VA. However, the SSA must consider the VA's disability determination when deciding your Social Security claim.