In January 1933, just before TVA was formed, the U.S. Army Corps of Engineers began work on Wheeler Lock and Dam to improve navigation on the treacherous upper Muscle Shoals and Elk River Shoals. When TVA was created that May, it took over construction of the project, with the U.S. Bureau of Reclamation and the Corps of Engineers continuing to work on the design. The lock was completed in 1935 and, after the reservoir filled, opened for operation on December 1, 1936. Measuring 60 feet wide, 360 feet long, and 53 feet high, it opened navigation on the Tennessee River at Wheeler Reservoir, which encompassed 67,100 acres, 74 miles of continuous navigable channel, a safe minimum depth of nine feet, and more than 1,063 miles of protected shoreline. On June 2, 1961, the lock's north land wall failed, severely damaging the lock and halting all shipping on the upstream 375-mile section of the Tennessee River. This hurt the region's economy and threatened the nation's space program because NASA's first Saturn rocket booster was to be shipped by barge through the lock from Redstone Arsenal in Huntsville, Alabama, to Cape Canaveral, Florida, for test firing that fall. TVA rebuilt a larger lock in less than a year. Completed in April 1962 and measuring 60 feet wide, 400 feet long, and 52 feet high, that rebuilt structure is now designated as the auxiliary lock. An even larger super lock, measuring 110 feet wide, 600 feet long, and 52 feet high, was completed in May 1963. As the primary navigational passage through Wheeler Dam, it continues to serve the growing demand for river commerce vital to the region's economic growth.