The Rolex and Tudor Underline Story

by Ross Povey - May 24 2018

Today we are taking a dive into the Rolex and Tudor underline story. The Rolex Sub has long been an iconic and collectible watch and now the Tudor Submariner is holding its own alongside its more expensive cousin. As collectors’ interest in a model grows, so does the focus on reference development and details. The Tudor Submariner 7928 is particularly interesting in this regard, as it follows many of the design elements on its coroneted cousin including case profile and dial types. Square, to pointed to rounded crown-guards are a development seen on the Rolex 5512 and the Tudor 7928. Additionally we saw chapter rings, gold lettering, dots and underlines on the dials of both marques during a roughly concurrent time-frame. There is nothing collectors love more than a small, but significant feature on a watch…its the little big things that count!


The Tudor Underline 7928

A Decade of Diver Development

We have a lot of love here at Bulang and Sons for the Tudor 7928 and we’ve sold quite a few interesting ones over the years. It was essentially Tudor’s response to their research and development work with the French National Navy, the Marine Nationale. The divers were having issues with the so-called Big Crown Submariners (7922 and 7924) leaking due to the large exposed winding crowns. The 7928 was introduced with crown guards to avoid the winding crown getting knocked and the rest is history…


Pointed Crown Guards – Protecting the Crown

Different Dials

We could write a whole article on the development of the dials, but today we are looking at one small detail. A small detail, but one that caused some of the world’s leading experts to debate its existence at length; its always the smallest details that cause the biggest discussions. We are, of course, talking about the small line that appears on Rolex and Tudor sports watches that collectors have called the ‘underline’. That does it mean? Why is it there? Let’s take a look.

The ‘Little Big Things’

Removing Radium

During the early 60s, watch brands began to recognise that radium was unsafe. The ‘Radium Girls’ were ladies who worked in dial manufacturing facilities in the United States, who died as a result of being exposed to radium whilst painting dials. Radium was commonly used for applications where luminescence was essential, for example clocks, watches and many military instruments. The girls were told to ‘point’ their paint brushes using their lips, instead of cloths to avoid unnecessary wastage. They developed terrible tumors on their faces and mouths and file lawsuits against their employers. For a while, radium was actually thought to have healing properties and so was used in drinks, toothpaste and even hair creams!

The Radium Girls

Good for you – Radium Water!

Still, however, it was used in watches until the early 1960s. Whilst the danger was (and still is) quite low for the wearer, who wears the watch with a sealed glass atop the dial, the considerable danger was to the manufactures and watchmakers.

Radiation Codes

Rolex had already recalled the bezels for the GMT-Master reference 6542 and had a replacement system in place for the bakelite inserts that were filled with radium. Rolex began marking their dials in around 1962 with features that indicated that the luminous was not full radium. This was important for dial storage and for those who were to handle the dials. The first appeared in 1962, by way of a small dot on the minute track at six o’clock. This signified a lesser amount of radium on the luminous compound on the hour markers on the dial. Collectors call these ‘exclamation dot’ dials, as the dot of luminous positioned below the narrow rectangular six marker on the dial looks like an exclamation mark.

Original Owner Tudor 7928 pointed crown guard gilt dial Submariner at Bulang and Sons

The Tudor ‘Exclamation Dot’ 7928

The Underline

The underline mark was another mark used to signify lesser radioactivity in the luminous mixture on the hour plots. For a good while, the debate raged about what exactly the small line meant. One theory was that it was a line to ensure the printing was aligned properly. Eventually it became accepted that it was there to identify the safer nature of the lume mix. From research undertaken, it seems that when tested, dials that feature the small underline do emit a much lower radioactive strength. The Geiger counter has become an essential tool for serious watch collectors and it is common to see dealers and enthusiasts alike, taking radiation readings at auction previews and watch fairs. It isn’t an exact science however! The 1963 Submariner with chapter ring, four lines of text and small underline was actually the last of the ‘SWISS’ only dials, before Tudor introduced the ‘T SWISS T’ designation at the bottom of the dial. As a safety measure these dials needed to be quickly identified as safe by those who needed to handle them or work on them; hence the unassuming and discreet underline.

Underline Above! The Underline appears in the upper half of the dial on this version.

The Rolex 5512 Underline

A nice little story about these Underline watches:
Years ago this 5512 Underline was still in the local shop of a friend in Maastricht. A client visited him from Spain.. especially for this watch. He and his lovely wife came all the way to inspect the watch. We talk years ago and way before the big value hype of the last years. The guy was just fully turned up and showing his wife the watch. “Look honey .. this Underline… so special and rare at this position”…  and he kept sharing his joy about this detail.
His wife looked at him and almost exploded..”What are you crazy, are you mad?? You pulled me all the way to the Netherlands, this small local town to talk and talk and get totally crazy about a 2 mm silver line ??? No Way !!!” She looked at him as if he was mad, full of pity.
Yes we call it true vintage Rolex Passion. It’s all in small details and variations, which make it all so fun. Let’s cherish our madness!

A  1963 Rolex 5512 Submariner with a very rare variation with the white SWISS and underline between the 4 lines.

Silver Underline – Applied on top of thelacquer


A amazing Rolex 5513 Underline with Double White SWISS print. Just like the Double SWISS Underline  1675 GMT below very very rare and in amazing condition.


A ref. 5500 Explorer with rare underline, SWISS only + T <25 markings

A 1950s Rolex 6538 Bigcrown with underline dial. So was the underline used before, or have full radium dials been swapped in the early 60th to less radiation dials? Would it have been done as replacement or did they still sell left over 6538 in the early 60th’s with a different dial. Magic of not knowing….


On the early Daytona ref 6239 

Case Shut

By 1963, the Submariner case had the pointed crown guards, which gives the watch a really sleek, vintage look that has an edge that is difficult to describe and portray in words and pictures, but easy to understand on the wrist. This combined with a cool rivet Oyster bracelet is a serious vintage watch! A four-line Rolex 5512 and  a Tudor 7928 alike, a roll of the wrist and catch the sun in just the right light…and BOOM!