Rolex Sea-Dweller Reference 1665: Tritium Dial vs. Rail Dial

The Rolex Sea-Dweller may not be the best-known Rolex timepiece. It indeed sits pretty behind the revolutionary Daytona, the Datejust, and the iconic divers’ watch Submariner.

However, the Sea-Dweller yet personifies what this elite Swiss-based manufacturer wishes to stand for.

sea-dweller reference 1665: tritium dial vs rail dial

The model has been in the market for the last 50years that was built originally to dive more in-depth than the Rolex Submariner being on the wrist of saturation divers.

Now, the Rolex Sea-Dweller reference 1665 of the late 1970s and early 1980s appear virtually identical at a glance.

However, the fact is that both watches have unique differences between them. And interestingly, the difference lies on their dial.

Today, let’s take a closer look at the Sea-Dweller 1665 with Tritium and Rail dials and find out the key features that make them unique.

The Rolex Sea-Dweller 1655: Tritium Dial

The name “Tritium” indicates a significant element of the dial. So, what is it?

Rolex applied a luminescent element “Tritium” to the early iterations of the Sea-Dweller. And, the material is radioactive.

  • Thus, the manufacturer wanted to indicate how much it has used the luminescent radioactive element.
  • Eventually, Rolex engraved code on the watch’s dial to specify it.
  • A Tritium dial consists of the “T” engraving under the 6 o’clock hour marker.

However, Rolex offered two types of Tritium dials to the Sea-dweller:

  • One, the Tritium Swiss- T <25 Dial
  • Second, the Tritium Swiss T <25 Dial.

The Swiss-T <25 designates that the watch is Swiss-made and has tritium levels emitting less than 25 mCi.

On the other hand, the T Swiss T<25 marking on the dial specify that the watch is Swiss-made and has tritium levels emitting less than 7.5 mCi.

However, it is significant to note that:

Some Sea-Dweller 1665 watches can flaunt only “Swiss Made” or “Swiss” markings on their dial.

This indicates that the watch doesn’t possess a luminous radioactive material.

Moreover, many service dials of later-era have “T Swiss T <25” markings. But the fact is they come with LumiNova hour markers.

Also Read: Review: The Refurbished Rolex Sea-Dweller

The Rolex Sea-Dweller 1655: Rail Dial

The Rolex Sea-Dweller Rail Dial is ideally much rarer than any other Sea-Dweller 1655 dials. Why?

The fact is that Rolex produced this Rail dial for only two years.

Between 1977 and 1979, Rolex produced the Sea-Dweller 1665 with the “Officially Certified” and “Superlative Chronometer” text engraved above the 6 o’clock hour marker.

If you compare both the dials, you will notice:

  • In Tritium dial, the letter “C” in “Chronometer” and “Certified” are not in line.
  • However, they are almost perfectly lined up or parallel on the Rail dial.
  • While the arrangement appears like the rails on a train track, it is dubbed as the “Rail Dial”.

The Rolex Sea-Dweller Rail dial is incredibly challenging to find.

They are found in vintage models, and also, Rolex has produced a very few examples of it in the first place.


The Sea-Dweller Rail Dial comes with a Tritium indication at the 6 o’clock position. You will notice that it features the “T Swiss T <25” marking.

Overall, the fact is that all Rail dials are also Tritium dials. On the contrary, all Tritium dials are not Rail dials.

Are you looking to sell our Rolex watch in London?

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You can sell your Rolex online in London or via appointment from anywhere in the UK. Regardless, we will make the process simpler and hassle-free, enabling you to raise cash within minutes.

Thus, to sell your Rolex Sea-Dweller or any other Rolex model to us,

  • Fill up this online form
  • Get a free competitive quote
  • Send your watch to us or book an appointment at our office in Hatton Garden, London for a final offer
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Also Read: Explore The ‘Star’ Vintage Rolex: The Double Red Sea-Dweller


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