at 400 locations before World War II. Many of these were licensed but not strictly franchised. Many closed during WWII. Between 1955 and 1967, another wave closed or caused changes in name. In 1967 the Kewpee licensor moved the company to a franchise system. Currently, only five locations exist. 1926: White Tower Hamburgers 1927: Little Tavern 1930s: White Castle (II; run by Henry Cassada) 1931: Krystal 1936: Big Boy. In 1937, Bob Wian created the double-deck hamburger at his stand in Glendale, California. Big Boy would become the name of the hamburger, the mascot, and the restaurants. Big Boy expanded nationally through regional franchising and subfranchising. Primarily operating as drive-in restaurants in the 1950s, interior dining gradually replaced curb service by the early 1970s. Many franchises have closed or operate independently, but at the remaining American restaurants, the Big Boy double-deck hamburger remains the signature item. 1940: McDonald's restaurant, San Bernardino, California, was opened by Richard and Maurice McDonald. Their introduction of the "Speedee Service System" in 1948 established the principles of the modern fast-food restaurant. The McDonald brothers began franchising in 1953. In 1961, Ray Kroc (the supplier of their multi-mixer milkshake machines) purchased the company from the brothers for $2.7 million and a 1.9% royalty. Today Hamburgers are usually a feature of fast food restaurants. The hamburgers served in major fast food establishments are usually mass-produced in factories and frozen for delivery to the site. These hamburgers are thin and of uniform thickness, differing from the traditional American hamburger prepared in homes and conventional restaurants, which is thicker and prepared by hand from ground beef. Most American hamburgers are round, but some fast-food chains, such as Wendy's, sell square-cut hamburgers. Hamburgers in fast food restaurants are usually grilled on a flat top, but some firms, such as Burger King, use a gas flame grilling process. At conventional American restaurants, hamburgers may be ordered "rare" but normally are served medium-well or well-done for food safety reasons. Fast food restaurants do not usually offer this option. The McDonald's fast-food chain sells the Big Mac, one of the world's top-selling hamburgers, with an estimated 550 million sold annually in the United States. Other major fast-food chains, including Burger King (also known as Hungry Jack's in Australia), A&W, Culver's, Whataburger, Carl's Jr./Hardee's chain, Wendy's (known for their square patties), Jack in the Box, Cook Out, Harvey's, Shake Shack, In-N-Out Burger, Five Guys,