Omega Caliber 1861: The Heartbeat of the Moonwatch

The Omega Caliber 1861 is a manual-winding chronograph movement, introduced in 1996 as the direct successor to the famed Caliber 861. It powered countless references of the Omega Speedmaster Professional, including the modern versions of the Moonwatch, and became one of the most recognized and celebrated movements in Swiss watchmaking.

Closely tied to NASA’s space legacy, the 1861 upheld Omega’s status as the only watch certified for manned space missions, maintaining the spirit of the movement that went to the Moon.

Technical Specifications

• Type: Manual-winding chronograph

• Functions: Hours, minutes, small seconds, chronograph (central seconds, 30-minute and 12-hour counters)

• Base: Lemania 1873

• Jewels: 18

• Frequency: 21,600 vibrations per hour (3 Hz)

• Power Reserve: ~48 hours

• Diameter: 27mm

• Chronograph: Cam-actuated, horizontal clutch

• Finish: Rhodium-plated (as opposed to copper plating in Cal. 861)

• Hacking Seconds: No

This movement retains much of the mechanical DNA of its predecessors—particularly the Lemania-based 861 introduced in 1968—but features an updated rhodium finish for better corrosion resistance and improved aesthetics.

Evolution of a Moonworthy Movement

The 1861 is the third-generation manual chronograph in the Speedmaster lineage, preceded by:

• Caliber 321 (column wheel, 18,000 vph) – Used in Speedmasters worn during Apollo 11

• Caliber 861 (cam switching, 21,600 vph) – Introduced in 1968 with the Speedmaster Professional

• Caliber 1861 – Introduced in 1996, based on the 861 with updated finishing

Omega chose to retain the cam-operated structure rather than moving to a column wheel, favoring reliability, ease of service, and proven resistance to shock—key features for a space-certified watch.

Watches Featuring Caliber 1861

The Caliber 1861 powered the Omega Speedmaster Professional “Moonwatch” from 1996 until 2021, including:

• Reference 3570.50 – The classic Moonwatch with Hesalite crystal and solid caseback

• Special limited editions – Apollo missions, Snoopy Award editions, and NASA tributes

• Speedmaster Professional with sapphire crystal – Paired with sapphire front and display caseback

The movement also appeared in Speedmaster Reduced and racing models, although in those versions, it was often modified or combined with automatic modules (as in Caliber 1140-series).

Performance and Legacy

Although basic by modern standards—no hacking seconds, no automatic winding—the 1861 remains beloved for its robustness and historic significance. It is:

• Extremely reliable under daily wear

• Easy to service, with ample parts availability

• Resilient under stress, proven in vacuum, G-force, and temperature testing

This movement is one of the very few mechanical calibers flight-qualified by NASA, and versions of the Speedmaster housing the 1861 were worn on the Space Shuttle, ISS missions, and EVA operations.

Replaced but Not Forgotten

In 2021, Omega replaced the 1861 with the Co-Axial Caliber 3861, which features:

• METAS Master Chronometer certification

• Co-Axial escapement

• Hacking seconds

• Silicon balance spring

• Improved anti-magnetism

Despite this technical leap, the 1861 is still celebrated by enthusiasts for its historical purity, hand-wound charm, and direct lineage to the Moon.

Final Thoughts

The Omega Caliber 1861 is more than a movement—it’s a mechanical legend. It ticks inside the watch that became the first worn on the Moon, and its design remained largely unchanged for over two decades. Collectors admire it for its proven spaceflight heritage, workhorse reliability, and connection to one of the most iconic timepieces ever made.

For anyone who owns or seeks a Speedmaster Moonwatch, the 1861 is a true piece of horological—and human—history.