To join the U.S. Army, you have to be between 17 and 34, with no more than two dependents, and pass the Armed Services' vocational aptitude test. As with all branches of the military, you have to have a high school diploma and pass a physical medical exam. You don't have to swim to join the Army, except for specific jobs.
All Army personnel have to pass a physical test that involves push-ups, sit-ups and running. Swimming tests are much less common and reserved for specialists. Army Rangers, for example, have to pass a tougher fitness test that includes a 15-meter swim in full military gear. The Army says when you're preparing for regular physical tests, swimming sessions can help toughen you up, but knowing how to swim isn't a requirement.