The Milsub Before the Milsub: Part 2 – Rolex Milsub A/6538A, a Special Edition for the Special Boat Service


When the first series of ref. 6538 Submariners was issued to the divers of the Royal Marines’ Special Boat Squadron (later to become the Special Boat Service), the divers noted one problem with the watch — it was difficult to rotate the bezel when wearing diving gloves. The Royal Navy also wanted the watch to have solid strap bars so Rolex decided to make a special model just for the SBS, initially carrying the unique reference 6540. This number would have made sense, as the ref. 6541 was the antimagnetic Milgauss, the ref. 6542 was the Mk1 GMT-Master and the ref. 6543 was the amagnetic Milgauss.

But as the quantity needed was so small — the initial order was for only 21 watches — it was decided to make these watches as a spin-off from the ref. 6538, and they were called the A/6538.

Nevertheless, this decision came rather late and the casebacks had already been made with the original model number stamped inside. So, all the A/6538 watches bear two references inside their casebacks, the original ref. 6540 neatly crossed out by three horizontal lines and their new model number next to it.

Such a small run of watches were obviously all made together and all bear the manufacturing date of the final quarter of 1957; no closer dating estimate can be made as all the ref. A/6538 watches have one other common trait — unlike all other Rolex Oyster watches, the ref. A/6538s are devoid of a serial number. I have handled five of the batch and none of them were numbered or showed signs of ever having a number between their lower lugs.


The A/6538 featured a more usable bezel design; one with much more pronounced ridges and it extended beyond the perimeter of the case, making it easier to grip whilst wearing diving gloves. Unlike the normal ref. 6538 bezels, which were made of a frangible rhodium-plated brass/zinc alloy, these bezels were made of German silver (an alloy of nickel, copper and zinc). The main advantage of this material was that when struck, it tended to dent rather than break. It proved to be such a success that it became the prototype for the bezels used on the ref. 5512/3 models, which followed soon after the ref. A/6538s, and has since been used on all subsequent Submariners.

The dials of the ref. A/6538 followed exactly the first dials from the civil ref. 6538, which is the Explorer configuration with three, six and nine o’clock in large radium numerals on a glossy black dial. There was one touch that Rolex added; instead of the usual “200m=660ft” printed in silver on the dial, these watches (and these watches alone) bore the legend “200/660” in red above the name “Submariner”, and there were no units printed after each number. This was the first time that Rolex had used red print on the dial of a sports watch, making the ref. A/6538 the holy grail for Submariner collectors; as it had the big crown, Explorer dial, military issue, unique model number and red print on the dial. In poker terms, it was a Royal Flush.

Radiation Hazard

Unfortunately, this unique dial did not survive for long. The problem was that it used radium as the exciter for the luminous material, and radium was a problem — both in nuclear submarines (where the users of these watches could be expected to travel and where it would trigger the sensitive radiation detectors used) and as a hazardous substance in its own right. In 1960, the MoD began to withdraw all watches with radium dials; they were sent to a specialist facility where the dial face with its radium-containing paint was brushed off under running water. The dials were then polished and reprinted by MoD contractor Watch Dials (Burford) Ltd (a subsidiary company of the Birmingham clock-dial restorers James Cooke & Son Ltd). They produced a reasonable facsimile of the original dials but these reprints had none of the delicacy and subtlety of the first run.

Here is an original ref. A/6538 dial.

An original ref. A/6538 dial
An original ref. A/6538 dial

And here is an MoD-refinished one.

A MoD-refurbished ref. A/6538
A MoD-refurbished ref. A/6538

It is easy to spot the similarity between the texts, with the same words and placements, apart from the circled letter “T” in the centre of the dial, which stands for Tritium, the new exciter for the lume on the dial. Tritium emitted only beta radiation, which is not only much less dangerous than the gamma radiation from radium, but could also be easily stopped by a watch crystal, hence cancelling the risk of radiation leak.

Even the earliest Submariners used on the first tests had their dials refinished by the MoD, which was determined that no radium dials would remain in its stocks; this ref. 6538 is extremely unusual in that it was never issued, even though the dial was refinished. Look at the condition of the case and bezel on the watch shown here.


You are probably wondering that if all the dials were repainted, how is there a photograph of an original dial in this article; that is worthy of an article in itself.

Detail shots of an ultra-rare MoD-refinished ref. A/6538

[Excerpted from an article by James Dowling, first published in September 2015]

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