Okubo served as director of the Art Students League from 1940 to mid-1942, when he was interned at the
Pomona Assembly Center outside Los Angeles. The momentum of Okubo's career came to a sudden halt when he was transferred to a
internment camp at the
Heart Mountain Relocation Center in
Wyoming following the
attack on Pearl Harbor during
World War II. While at the camp he instructed a life class. He and fellow artist
Hideo Date also initiated evening and Saturday art classes, which they referred to as the Art students league of heart mountain. Date soon withdrew from teaching, but Okubo taught until his release in September 1945.
Estelle Peck Ishigo was one of his students. Chisato Takashima was another student, and they married in
Billings, Montana on June 12, 1945. == Later life ==