In addition to teaching, he was named Director of the Busch-Reisinger Museum there, which was dedicated to the study of art from Germanic countries, succeeding Kuno Francke.
During his tenure, Kuhn helped the museum acquire important works such as Self-Portrait in Tuxedo by Max Beckmann.
Kuhn's academic career was interrupted by World War II as, in 1942, he joined the United States Naval Reserve as a Navy Intelligence Officer.
In addition to rising to the rank of Lieutenant Commander, he was also assigned an Officer for Monuments, Fine Arts, and Archives program (MFAA) by the Roberts Commission.
In 1945, Kuhn was named Deputy Chief of the MFAA by its head, Geoffrey Webb, and was stationed in Frankfurt and Versailles.