The Office of the General Counsel has a limited number of spots for summer interns after their first or second year of law school. These spots are filled through the US Army JAG Corps summer internship program. A JAG Corps summer internship does not, in itself, incur a service obligation. Note that, in most cases, in order to be eligible for assignment to the Pentagon, a summer intern will need to have a security clearance already in place.
To learn more and to apply, go to "Summer Intern Program" on the JAG Corps website.