In the spring of 1972 Lockheed Aircraft, McDonnell Douglas, Grumman, and North American Rockwell submitted proposals to build the shuttle. The NASA selection group thought that Lockheed's shuttle was too complex and too expensive, and the company had no experience with building manned spacecraft. McDonnell Douglas's was too expensive and had technical issues. Grumman had an excellent design which also seemed too expensive. North American's shuttle had the lowest cost and most realistic cost projections, its design was the easiest for ongoing maintenance, and the Apollo 13 accident involving North American's command and service module demonstrated its experience with electrical system failures. NASA announced its choice of North American on 26 July 1972.