After 1900, the Port of Galveston emerged as the second largest in the U. S. Following completion of a deep-water channel to Texas City in 1904, the Mainland's major petroleum and petrochemical plants, tin smelter and allied industries had their beginning. Galveston's waterfront handles primarily dry cargo while Texas City handles liquid petroleum and petrochemical cargoes. Agriculture production is also important to the Galveston County economy. Rice, corn, grain, oats, dairying, poultry, truck crops and cattle raising are leading items. In 1913, the U. S. Army moved 10,000 men and eight of its twelve airplanes to Texas City, with the first successful test flight made from Texas City to San Antonio. In 1928, Galveston County began initial seawall protection for Texas City. Following the devastating effect of hurricane Carla in 1961, construction began on a 17-mile protective system extending around Texas City and LaMarque. Disaster struck Texas City, April 16, 1947, with the explosion of the French-flag steamer "Grandcamp." Resulting fires and explosions left 576 dead, 4,000 persons injured and $70,000,000 property damage. Undismayed, the city rebuilt. In addition to its port facilities, Galveston is a large supplier of seafood, is a major financial center, has a tea-blending plant, a rail and wire factory, grain elevators, a brewery, several large insurance companies, a ship repair yard and many part-associated industries. A servicing facility for nuclear-powered commercial vessels is also maintained here.' A major contributor to the Galveston economy is the University of Texas Medical Branch. Created in 1881, the facility is known as "The Mayo's of the South" and is a leading heart, surgical and burns treatment center. The Galveston County Memorial Hospital was constructed on the Mainland in 1952. With the establishment of the National Aeronautics and Space Administration's Manned Spacecraft Center in 1961 at Clear Lake, bordering Galveston and Harris counties, many residents of Galveston County became employed in the space effort. Space vehicles and equipment were tested in nearby Galveston Bay.