Larger and larger lake freighters were carrying the ore vital to the war effort, and it was determined that a new, longer and deeper lock had to be built to replace the now obsolete Weitzel Lock. The St. Mary’s River had been dredged during the 1930s to 24 feet, but the Poe and Sabin Locks, which handled most of the traffic on the American side, couldn’t accommodate boats drawing more than 20 feet.
Congress ordered construction of a new lock on March 7, 1942, to replace the old Weitzel with one that would handle the new breed of freighters. The new lock would be named after Douglas MacArthur, the war hero of the Pacific theater. Previously, the Weitzel and Poe Locks had taken eight years to build; the Davis Lock, six. But this was wartime, and the new lock had to be built ASAP.
Work began on September 1, 1942, as the initial cement forms were laid. Crews of the Great Lakes Dredge and Dock Company worked around the clock. When temperatures plunged below zero during the frigid winter months, heaters had to be employed to allow the cement to set. Work on the MacArthur Lock was completed in a mere 16 months, and dedication ceremonies were held on July 11, 1943. The first boat through the new lock was the Carl D. Bradley. The contractor and its workers received the Army–Navy E Award for their efforts in building the crucial new lock in record time. The estimated 1,000-plus construction workers added to the housing burden that already had tiny Sault Ste. Marie bursting with soldiers.
Rachel North, “Northern Michigan History: When the Soo Locks Readied for World War II“, UpNorth, February 18, 2014.