Just prior to World War II, the Civil Aeronautics Administration (CAA) selected the site as an important civil air field and negotiated a standard agreement (AP 4) with the county of San Bernardino to maintain the air field. Shortly thereafter, the site was chosen by the War Department as a Modification Center. As a result, the county acquired fee interest to the additional land necessary for War Department use. On 4 May 1942, the government entered into an agreement with the county to lease the 1,099-acre site (renewable annually but not beyond 30 June 1967).