Deep Dive: What are the most important mechanical Swiss watch movement ever?

Defining the single "most important" mechanical watch movement is challenging, as several calibers hold this status for different reasons—from enabling human spaceflight to reviving the entire Swiss watch industry.

Based on their profound historical impact, five movements are particularly strong contenders. The table below summarizes why each is significant.

Movement	Movement Key Claim to Importance	Notable Watches & Legacy
Lemania 2310 (Cal. 321)	The moon landing caliber: Foundation for Omega's Cal. 321, the first watch worn on the moon	Omega Speedmaster, Patek Philippe perpetual calendars
Jaeger-LeCoultre 920	The ultra-thin enabler: Thinnest full-rotor automatic movement; made the first luxury steel sports watches possible	Audemars Piguet Royal Oak, Patek Philippe Nautilus, Vacheron Constantin 222
ETA 2824-2	The universal workhorse: Mass-produced, reliable movement that powered countless brands for decades	Used by hundreds of Swiss brands; inspired the Sellita SW200 clone
Zenith El Primero	The high-beat survivor: First integrated automatic chronograph; kept high-frequency mechanics alive during the Quartz Crisis	Zenith Chronomaster, Rolex Daytona (early models)
Rolex Caliber 3135	The modern icon engine: Paragon of robustness and serviceability that powered Rolex's most iconic watches for 30+ years	Rolex Submariner, Datejust, Sea-Dweller

Deep Dive: Important Japanese Mechanical Watch Movements

 

From a purely mechanical perspective, Japanese watchmaking's most significant contributions are different in character from the Swiss "most important" movements. While Swiss contenders are famous for their historical events or design influence, Japan's strength lies in democratizing quality, relentless innovation, and achieving a unique synthesis of technologies.

The following table summarizes the three most significant Japanese contributions to mechanical watchmaking.

Key Japanese Contribution	Primary Significance	Notable Movements & Legacy
Seiko's Accessible & Robust Mechanics	Democratized automatic watch ownership with reliable, affordable movements.	7S26/4R/NH Series: Workhorse movements powering millions of watches (e.g., Seiko 5, SKX divers). Proprietary Tech: Magic Lever (efficient winding), Spron alloys (durability), Diashock (shock resistance)
Citizen/Miyota's Ubiquitous Workhorses	Powered the global microbrand revolution as a reliable, off-the-shelf engine.	Miyota 8215/9015: Mass-produced, reliable automatic movements used by hundreds of brands worldwide. Citizen develops its own in-house mechanical calibers as a true manufacturer.
Grand Seiko & Credor's High-Horology	Proved Japan could rival Swiss precision and craftsmanship at the highest levels.	Spring Drive (cal. 9R): A unique hybrid, using a mainspring regulated by a quartz-crystal-controlled "glide wheel" for exceptional accuracy (±1 sec/day). Hi-Beat (cal. 9S): High-frequency mechanical movements (36,000 BPH) for superior precision.

Marathon GPM Government Black Mechanical Reference WW194003BK, Rough & Tough, A Review (plus Video)

Prior to the Covid-19 lock-down in Kuala Lumpur, I got myself a well-known military watch from a famous Canadian brand, Marathon. The Marathon GSAR Government Diver Automatic WW194006 was purchased from Gnomon Watches of Singapore back in March 2020 (The link to that watch can be found here). That watch is a famous dive watch by Marathon. 

Another iconic design by Marathon is the GPM or General Purpose Mechanical model, a field watch. I decided to get one also and I chose the reference WW194003BK for the collection. This watch is a subject of this review.

This field watch is issued to entitled military personnel especially those serving with ground forces. A no-frill timepiece, the watch provide the two basic tenets of is specifications - accuracy and simplicity. The specifications is based on the US Government Standard MIL-W-46374 specifications which states that a timepiece fulfilling this standard must need to have: 15 jewels (or more) mechanical movement; at least 36 hours of power reserve; has a hacking mechanism; shock resistance; water resistance of at least 30 meters or more; have nylon straps; and have luminous hands and markers that have to glow for 8 hours or more in total darkness. There are other requirements but the one listed above are the primary ones under the standard.

Orient Star Open Heart Tonneau DAAA004W or WZ0121DA (other options DAAA002T/WZ0131DA, DAAA003B/WZ0151DA & DAAA001W/WZ0141DA) – A Suave Timepiece, A Review (plus Video)

This is my first tonneau shaped wristwatch. The Orient Star Open Heart Tonneau with reference number DAAA004W (or WZ0121DA in Japan) has a vertical cross-section barrel shaped casing seldom used by watch manufacturers due to a number of reasons. It has the classical aura of a formal timepiece which I find very appealing. This particular model was released back in April 2014.

Age must be getting to me. During the start of my watch collection hobby I was keened on dive or sports watches. Formal or dress wristwatches were seldom in my radar. However, in recent times, my interest in dress watches started to grow and I have been shifting my focus towards that genre ever since.

The Orient Star Open Heart Tonneau is a stainless steel construction with polished and brushed surfaces. It has mirror finished top surface and a matte finished side. It has a curved sapphire crystal glass with anti-reflection coating protecting the dial and a flat crystal glass as a display case-back. The case-back panel is attached to the watch casing via four screws. The signed push-in crown is located at 3 o’clock and the watch comes with a power reserve complication. It is powered by an automatic engine that can be manually wound. The wristwatch is paired with a black matte calf leather strap with crocodile embossing and signed buckle.

Movement: The Miyota 8205/8215 automatic

The Miyota 8215 (and its other variants such as the 8205) is a Japanese automatic wristwatch movement that is used by many watch makers. Miyota is part of the Citizen group of companies.

The Miyota 8215 is a non-hacking twenty-one (21) jewel three-hand with date movement with a uni-directional winding system (left rotation) with an accuracy of -20 to +40 seconds per day, and a power reserve of over 40 hours. The diameter of the movement is 26 mm and the thickness is 5.67 mm. It beats at 21,600 BPH or 3 Hz (6 half-cycles per second).

Below are some technical information useful for the understanding of the movement.

The specification of the Miyota 8205/15/0A/1A movement by Meor Amri

Blueprint of the Miyota 8215/821A movement by Meor Amri

Spare parts reference for the Miyota 8205/8215 movement by Meor Amri

My watches that uses the movement (or its variants) are:

1. MWF-Gruppo Gamma LE Watch; 
2. Citizen Promaster Autozilla 1000m Titanium Divers Watch NH6930-09F (NH6931-06E);
3. Citizen NY0040 200m Promaster Diver; and
4. Citizen Automatic NY602151E Divers' Watch 

I have not had any problems with the mechanism throughout the years. From a practical point of view, the accuracy is more then sufficient for normal timekeeping duties although some may argue its 'lack' of accuracy compared to other movements from Switzerland and Japan.