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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; Mo Rocca discusses a biography of entertainer Desi Arnaz, who co-starred with wife Lucille Ball in the classic sitcom “I Love Lucy”; Patrick Gaffigan offers his thoughts on his dad, comedian Jim Gaffigan; and Conor Knighton learns the magic behind “worm grunting.”