Celebrating Father's Day, David Letterman and IndyCar Racing, U.S. Army Turns 250

Hosted by Jane Pauley. In our cover story, David Pogue looks at the legacy of singer-songwriter, activist and father Harry Chapin. Plus: David Martin examines the origins of the U.S. Army as it marks 250 years; Tracy Smith explores the allure of auto racing with Indy Car team co-owner David Letterman; and Conor Knighton learns the magic behind “worm grunting.”