Hackett saw active service in the engagements at St. Mihiel and the Argonne. On September 28, 1918, near Very, France, he suffered wounds that almost claimed his life. In his war diary, "The Cannoneers Have Hairy Ears," Robert J. Casey, who served under Hackett as a Captain and later became an award-winning columnist for the "[[Chicago Daily News]]", described the severity of Hackett's injuries and his long and difficult recovery: