Christmas Day intrusion into the grounds of the White House complex. Although he eventually surrendered, Fields threatened White House security during negotiations that lasted for four hours. Along with an intrusion by Robert K. Preston in February of the same year, this incident sparked a security review by the U.S. Secret Service.
The White House's physical security measures following World War II were oriented against intrusions by individuals and assassins. As a prelude to Fields's breach of security, in February 1974, Private Robert K. Preston, a U.S. Army helicopter mechanic, managed to steal a military helicopter from Fort Meade, Maryland. He briefly touched down in the South Lawn after flying over the Executive Mansion. In addition, in 1973, another individual had attempted to crash his vehicle through the White House gates.
On December 25, 1974, Marshall Fields crashed his Chevrolet Impala into the Northwest Gate of the White House complex. Dressed in Arab clothing, Fields claimed that he was the Messiah and that he was laden with explosives. He drove up to the North Portico and positioned himself only several feet from the front door. After four hours of negotiations, Fields surrendered. The explosives he claimed to be in possession of were discovered to be flares. President Gerald Ford and his family were not home at the time.
As a result of this attack, the Secret Service began to review their security measures. Although spokesperson George Cosper claimed that the White House's security was adequate, the 19th century wrought iron gates were replaced in 1976. Later that year, Stephen B. Williams attempted to drive his pickup truck into these new gates. Although the front of his truck suffered damage, the gate held. Since then, several others have attempted, but none have succeeded in mimicking these attacks.