“No legs, no gags, no chance,” the producer Mike Todd famously assessed a new show that was trying out in New Haven. But when this particular turkey opened in New York, police had to hold the crowds back from the box office. It ran for half a decade. It won a special citation from the Pulitzer Committee. And it changed the musical theater forever. On the fiftieth anniversary of Oklahoma! John Steele Gordon tells what made it the most important musical in Broadway history.