To outfit Afghanistan’s security forces with new helicopters, the Pentagon bypassed U.S. companies and turned instead to Moscow for dozens of Russian Mi-17 rotorcraft at a cost of more than $1 billion. Senior Pentagon officials assured skeptical members of Congress that the Defense Department had made the right call. They repeatedly cited a top-secret 2010 study they said named the Mi-17 as the superior choice. Turns out the study told a very different story, according to unclassified excerpts obtained by The Associated Press. An American-made helicopter, the U.S. Army’s workhorse Chinook built by Boeing in Pennsylvania, was found to be...