It is not often that visitors to the Smithsonian’s National Air and Space Museum are interrupted by the strains of Johann Sebastian Bach.

Starting with a single cellist in the middle of the museum’s “Milestones of Flight” gallery and swelling to 120 musicians, the U.S. Air Force Band exhilarated museum visitors yesterday with the first flash mob to be produced by one of the five military branches’ top bands.

The four-minute performance featured an original arrangement of Jesu, Joy of Man’s Desiring/Joy to the World led by the band’s commander Col. Larry H. Lang.

Unsuspecting museum visitors were astonished as instrumentalists streamed into the gallery from behind airplanes and space capsules, and vocalists burst into song from the museum’s second-floor balcony.