Seamaster Aqua Terra 150M Co-Axial 39.2 Railmaster Yellow Gold / Bracelet

In Context

At 39.2 mm it sits just under the modern norm — the band that suits the widest spread of wrists. The case back is open, so the movement is visible without taking the watch apart, and the sapphire crystal will resist everything short of deliberate abuse. 150 m is genuine swimming resistance — more than the shape of this watch suggests it would need.

The movement winds itself from the motion of your wrist. 48 hours of reserve is enough to set it down on Friday evening and find it still running on Monday. At 25,200 vph the seconds hand advances 7 times a second.

2103.52.00 stands on its own in this catalogue — no other reference here shares its base number. It pairs a black dial with a yellow gold case.

The 2403 is the 2500 without a date, the co-axial movement Omega fitted to the Railmaster of 2003 and the Museum Collection reissues. It powers 38 watches in this library. The [2500](/calibers/omega-2500) is the ETA 2892-A2 rebuilt around the co-axial escapement, with 27 jewels, a 48-hour reserve and a beat of 25,200 vph, certified by the COSC. Leaving the date out suits watches drawn from the 1950s, whose dials never had a window, and it gives the crown one position fewer. The [2892 piece](/blog/the-eta-2892) explains the base. In the library it sits under 18 Museum Collection references, the numbered reissues of historical Omegas made in the 2000s, 14 [Railmasters](/brands/omega/railmaster), the 39.2 mm and 42.2 mm anti-magnetic models of 2003, 4 [De Villes](/brands/omega/de-ville) and 2 [Constellations](/brands/omega/constellation). The 37 mm Museum Collection case accounts for 18 references and the 39.2 mm Railmaster for 9. 21 of the 38 are limited editions. The [8806](/calibers/omega-8806) is the no-date Master Chronometer movement in the current Railmaster, and the [2627](/calibers/omega-2627) the 2500 derivative with a power reserve indicator.

37 other watches in the library run the Omega 2403.

Omega

Museum Collection Seamaster XXIX / 2008 Beijing Olympics Day 11

516.53.37.20.09.018 · 37 mm

Omega

Museum Collection Seamaster XXIX / 2008 Beijing Olympics Day 1

516.53.37.20.09.008 · 37 mm

Omega

De Ville Co-Axial 44 Red Gold / Opaline

4658.30.32 · 44 mm

Omega

Seamaster Aqua Terra 150M Co-Axial 39.2 Railmaster Yellow Gold / Brown Alligator / China

2108.52.00 · 39.2 mm