Photo by metrodcphotography.

Tourists and space enthusiasts visiting the Smithsonian’s Air and Space Museum yesterday were treated to a surprise: The U.S. Air Force Band went all “Improv Everywhere” and gave a “flash mob” impromptu performance.

In the middle of the museum’s “Milestones of Flight” gallery, a single cellist sat down and started playing, as more and more members of the band came to join him, until there were 120 musicians performing. According to a press release, this was “the first flash mob to be produced by one of the five military branches’ top bands.”

The band gave a six-minute performance, which featured an original arrangement of “Jesu, Joy of Man’s Desiring/Joy to the World.” The flash mob was held to promote the band’s schedule of free holiday performances, which you can view here.

Here’s video of the performance.