Seiko Prospex MarineMaster 'MM300' Diver's Automatic Blue Ocean Dial Silver Stainless Steel Men's Watch SLA023J1
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Seiko Prospex Marine Master 'MM300' Diver's Automatic Blue Ocean Dial Silver Stainless Steel Mens Watch SLA023J1
Style:
Functions:
Made In Japan:
Firstly, for all you Seiko enthusiasts, this premium timepiece has been made in Japan, indicated by the suffix ‘J’. Seiko watches made in Japan are hard to obtain outside of Japan due to the highest quality of craftsmanship and astonishing features that come in each individual timepiece. We have a range of Japanese watches here at Watchnation but in limited quantities, so if you are looking to add to your collection then this is the perfect place for you.
Key Features:
| 8L35 Caliber | Auto + Manual Winding | +15 to -10 Seconds Per Day |
| 50 Hour Power Reserve | Stainless Steel Case | Ceramic Bezel |
| Sapphire Crystal | Anti Reflective Coating | Lumbrite Hands & Indexes |
| 3 Fold Clasp & Lock | 300m Water Resistance | One Piece Structure |
| Screw-down Crown | Undirectional Rotating Bezel | 26 Jewels |
| Date Display | Stop Second Hand Function | Free Rubber Strap |
The Prospex Story:
Scuba-diving became increasingly popular around the 1960’s, an example of this was the formation of the Professional Association of Diving Instructors (PADI) in 1965. Moreover, diving equipment was becoming increasingly reliable, so more people began to dive recreationally. There was of course a crucial need for divers to be able to time their dives. Subsequently, the watch market responded to this necessity by flooding the market with reliable dive watches.
In 1965, Seiko first produced their original dive watch - the 6217. This was the very first Japanese dive watch and it paved the path for future divers that claim to meet Seiko’s Professional Specifications. The original 6217 was notably worn by the 8th Japanese Antarctic expedition. This model featured bidirectional rotating bezel, legible lumed hands, and an easy-to-grip crown.
Although professional divers were still pining for a dive watch that had the capability of going deeper than 300 metres. The Seiko development team went about going to produce a watch which was capable of doing so. The year 1975 marks the release of the first Seiko Prospex, with the ability to be used in 600 metres of depth. The Prospex is the first diver watch to use a titanium case instead of standard steel. It was also the first to use a ceramic shroud for deep-sea diving and the first to use a hybrid analog digital watch with an alarm.
Another achievement for the Prospex family was the L-shape single crystal gasket, which prevented any helium escape valve unnessacary. This was one of the development teams first aims, to prevent a helium resistant watch. There were numerous other milestones that Seiko achieved with the Prospex. Such as in 1986 when Seiko produced a watch that was water resistant to 1000 metres.
The Brand: Seiko
Seiko’s story began in 1881 with the opening of a shop in Tokyo, it’s owner was Kintaro Hattori. Eleven years after the opening of his shop, Hattori opened a clock factory in 1895 that they began to produce pocket watches. Soon followed by alarm clocks in 1899, and then table clocks in 1902. Then in 1913 Hattori began working on his first wristwatch. Then in 1924, the brand Seiko was born with the creation of the first Seiko wristwatch.
Seiko established itself throughout the 20th century as being a force in the advancements that took place in the watching world. For example, Seiko were the producers of the first winding wristwatch made in Japan. Then in 1964, Seiko became the official timer for the Olympics. And then most notably Seiko unveiled the first quartz wristwatch, the Astron, in 1969. Marking the beginning of the quartz revolution. Or equally impressive the creation of the world’s first TV watch in 1982. And even more relevant today, with our abhorrent use of non-renewable energy sources, Seiko’s Kinetic. This watch had the ability to generate its own power from the movement of the wearer.
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UK Delivery
| Selling Price | Royal Mail 48 (Tracked) |
Royal Mail 24 (Tracked & Signed) |
Special Delivery Next Day (Mon – Fri) |
Special Sunday Delivery (Before Sat 12pm) |
Royal Mail Special Delivery by 1pm |
|---|---|---|---|---|---|
| £0 to £99.99 | FREE | £4.99 | £7.99 | £7.99 | £9.99 |
| £100 to £499.99 | N/A | FREE | £7.99 | £7.99 | £9.99 |
| £500 or more | N/A | N/A | FREE | £7.99 | £9.99 |
We know your order is important to you, so we use Royal Mail’s tracked delivery service on all UK orders.
We also offer Royal Mail Special Delivery service, which for an additional fee offers guaranteed delivery the next day before 1pm.
*Royal Mail Tracked 24 and Royal Mail Tracked 48 services are 98% accurate but not guaranteed.
Orders placed before 5pm (Monday–Friday) are dispatched the same day. Orders placed on Saturday or Sunday are dispatched the following Monday.
International Shipping & Duties (Delivered At Place – DAP)
We’re pleased to offer worldwide delivery with fully tracked and insured shipping.
How international orders work
All international orders are shipped on DAP (Delivered At Place) terms. This means:
- The price you pay at checkout covers your goods and international shipping only.
- WatchNation does not collect or charge any overseas sales tax, import VAT, or customs tariffs (duties).
- When your order reaches your country, local customs authorities may apply:
- Import VAT (value-added tax),
- Tariffs or customs duties (import taxes based on product category and value), and
- Handling or clearance fees from the courier.
These charges are set by your country’s customs authority and are payable by you before delivery.
You’ll be contacted directly by DHL with a secure link to pay any applicable charges. Once cleared, your parcel will be released and delivered promptly.
Estimated delivery times (after dispatch)
- European Union: approximately 2–5 working days
- Rest of World: approximately 5–7 working days
Customs processing times vary by country and may extend delivery slightly.
If import charges, tariffs, or duties are not paid
If local charges are unpaid or delivery is refused, the shipment will be returned to us. In this case, we will refund your order minus the outbound shipping cost and any return or customs fees billed to us by the carrier.
Estimating import costs
Import VAT and duty rates vary by country. You can check estimated import taxes and tariffs by contacting your local customs authority or using your government’s online import calculator.
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Frequently Asked Questions
Yes — we are an Authorised Dealer for every brand we sell. All watches come with an official box, papers, and a full manufacturer’s warranty.
Every watch includes a manufacturer warranty. You’ll find more warranty info listed in the product description.
Orders placed before 5pm (Mon–Fri) are dispatched the same day. Order before 12pm on Sat for same-day dispatch. Free UK delivery is available on all orders, and tracking details are provided once shipped.
Yes — you have 30 days from delivery to return or exchange your item, provided it’s unused and in its original packaging.