The explosion of the enormous floating rig Deepwater Horizon and the ensuing oil spill into the Gulf of Mexico is well known as the worst environmental disaster in U.S. history. A buried truth within that statistic is that 11 workers lost their lives in April 2010, when pressure built up in a pipeline submerged a mile underwater, resulting in a massive blowout and fire. “Deepwater Horizon” revisits that tragedy, reconstituting it as both a rousing action movie and a somber memorial to the dead.