Robert remained close to his brother John in death as well as in life.

Robert Douglas Christiansen was born in Santa Cruz, California, on May 3, 1949, to Mr. and Mrs. Gerald B. Christiansen. He was raised in the family home on Pine Flat Road in nearby Bonny Doon, California. It is unclear whether his brothers John, Michael, Bruce and Richard and sisters Mary, Donna and Janet all lived together at that location at the same time. He attended local elementary schools and may have attended San Lorenzo Valley High School in Felton. During his time in Santa Cruz County, Christiansen worked at Spivey's, a popular local restaurant, and at the Dream Inn Hotel.

About 1968, Robert Christiansen moved to Oklahoma City, Oklahoma, where he joined the US Marine Corps. He received his basic and school-of-infantry training at Camp Pendleton, California and qualified as an infantry rifleman.

Lance Corporal Christiansen arrived in Vietnam on January 11, 1969, and was assigned to Company A, 1st Battalion, 9th Marine Regiment of the 2nd Marine Division stationed at the Da Krong Valley base in Quang Tri Province. After only a month with his unit, Robert's company received orders to participate in Operation Dewey Canyon.

“Operation Dewey Canyon was the last major offensive by the United States Marine Corps during the Vietnam War. It took place from January 22 through March 18, 1969 and involved a sweep of the North Vietnamese Army (NVA) dominated A Shau Valley by the 9th Marine Regiment reinforced by elements of the 3rd Marine Regiment.”

On February 21, 1969, while on a patrol thirty-four miles south of Vandergrift Combat Base near Ca Lu, Lance Corporal Robert Douglas Christiansen suffered fatal wounds to the head from enemy mortar fire. His body was recovered and returned to California where he was buried in the Golden Gate National Cemetery in the plot next to his brother, former Army Private John Todd Christiansen, who had died July 18, 1966, after leaving the service.

(VVMW; UDVA; WIKI, Dewey Canyon; US Marines Combined Action Platoons CAC/CAP, Vietnam 1965-1971 http://www.capmarine.com/, [16 September 2008]; SCSn February 28, 1969)