Caliber 321 is the column-wheel manual-wind chronograph movement produced by Omega from 1946 to 1968. Originally developed in collaboration with Lemania (as the Lemania CH27 C12), the Caliber 321 powered the original Speedmaster references including the CK 2915, 105.002, 105.003, 105.012, and 145.012. Apollo 11 astronaut Buzz Aldrin Speedmaster — worn on the lunar surface — contained a Caliber 321. Omega retooled the Caliber 321 for limited modern production beginning in 2019.

Caliber 321 is a chronograph movement produced by Lemania and used by Omega in the original Speedmaster from 1957 through 1968, including the references that flew on NASA’s Apollo missions. The movement is a column-wheel chronograph hand-wound calibre measuring 27 millimetres in diameter, derived from the Lemania 2310 architecture. It is widely regarded by watchmakers as one of the finest chronograph movements of the twentieth century.

Calibre 321 was replaced in production by the cam-actuated Calibre 861 in 1968. Omega reintroduced the calibre in 2019 in a limited modern production run, but vintage Speedmasters powered by the original 321 — particularly the 105.012 and 145.012 references that crossed over with the lunar landing era — remain the most coveted by chronograph collectors. See our Speedmaster 105.012 item entry for a specific example and our most collectible vintage chronographs list for context.