Omega Seamaster 501 automatic, 1956

Last Updated on April 26, 2025 by Jason

This vintage Omega Seamaster wristwatch has a calibre 501 20-jewel automatic movement that works well and keeps time accurately. The movement is fully signed by Omega, and the serial number 15,832,615 dates back to 1956. The Seamaster is one of those iconic brands that every true watch connoisseur wants to have in their collection. I am no different, the Seamaster is a “must-have” vintage watch. In this post, we take a look at a relatively early Omega Seamaster in stainless steel, with one of the most reliable automatic movements from the 1950s & 60s, the Omega calibre 501.

Vintage Omega Seamaster wristwatch, 1956.

The Omega Seamaster brand

The Omega Seamaster was introduced in 1948 to celebrate Omega’s 100th anniversary. It quickly established itself as a watch that was durable, precise and elegant. Drawing on the waterproof innovations developed for the British military during World War II, Omega unveiled the Seamaster 300 in 1957. It was embraced by pioneering divers such as Jacques-Yves Cousteau and his Calypso team. Over the decades, the line continued to evolve, adding the helium escape valve of the “Ploprof” in 1970 and the modern Planet Ocean series in the 2000s, rated to 600 meters. Its blend of technical innovation and elegance earned it fame as James Bond’s watch of choice beginning with GoldenEye in 1995. Today, the Seamaster line, from the classic Aqua Terra to the rugged Planet Ocean, remains a cornerstone of Omega’s legacy, blending tradition, innovation, and adventure.

Seamaster logo

The Omega engraver Jean-Pierre Borle conceived the Seamaster’s hippocampus logo, often called the “seahorse”, in 1958. He drew inspiration from the ornate sea-horse (hippocampi) decorations on Venetian gondolas during a trip to Venice. The design, a mythical creature with a horse’s upper body and a fish’s tail, connects to ancient Greek/Roman mythology and represents protection at sea. It was first stamped on the case backs of Seamaster models in 1958 to symbolise their water-resistance. However, this particular watch pre-dates the release of the logo by two years and has a plain case back.

Omega calibre 501

The Omega calibre 501 was in production from 1955 until 1960. It was the first full-rotor driven movement produced by Omega. Earlier examples of Omega automatics used the less efficient “bumper” movement, of which the most famous was the 350 series (1945 to 1949).

The calibre 501 is a 28 mm automatic movement, featuring a piggy-back winding module on a hand-wound base. It originally included 19 jewels, but later models such as this example had 20. The movement operates with a frequency of 19,800 vph, Incabloc shock protection and a power reserve of 46 hours.

Typically, the calibre 501 was COSC-certified for Constellation models but also saw use in some Seamaster references (e.g. 2846-1 SC). Its modular construction made it interchangeable with other 500 series calibres. Today, collectors respect the calibre 501 for its accuracy and robust longevity.

Case

The watch case measures 34mm in diameter, excluding the winding crown and the lugs. The case is “Denisteel” stainless steel, and it is in good condition with just some light marking and a little gentle unevenness to the back. This is nothing more than patina and adds to the character of the watch. The inside of the case back has the Omega logo. As a nod to authenticity and originality, the watch has the original signed Omega Seamaster winding crown. The unsigned acrylic crystal lens is in good condition. The silver two-tone dial has light freckling. The watch comes with the original dauphine-shaped hands and centre seconds hand.

Denisteel case

The Dennison Watch Case Company registered the Denisteel trade name in 1934 to describe its stainless steel watch cases. Harry Brearley of Thomas Firth & Sons developed stainless steel in 1912. Initially, stainless steel was used for cutlery. However, by the 1930s, due to the Great Depression, watchmakers began to look for cheaper alternatives for watch cases than gold, silver and even nickel. As a result, watch cases began to be made from stainless steel in the early 1930s. Today, we most commonly find the Denisteel stamp inside case backs from the 1940s to the 1960s on UK market models by Omega, Rolex and IWC.

Omega Denisteel cased models were assembled in Handsworth, Birmingham. They made use of imported Swiss made Omega dials and movements. This was to avoid the costly import fees on cased watches from Switzerland. To avoid this surcharge, brands would export bare movements to the recipient country and allow authorised dealers to case the movements in local cases. Dennison cases in particular were very similar to the official Omega models, which is no accident, as they were officially sanctioned by Omega and produced to Omega technical specifications.

The case back is Stainless Steel and is in good condition. Inside, it is signed: “Pat. Applied For, Omega Watch Co, Denisteel, Made in England, Fit washer in back”.

Beads of rice bracelet

The watch comes on a “beads of rice bracelet” made of stainless steel. The “beads of rice” bracelet was originally designed by the renowned Swiss bracelet-making company, Gay Frères. Founded in 1835, Gay Frères became famous for creating high-quality watch bracelets for many prestigious watch brands, including Omega, Patek Philippe, and Rolex. The distinctive design gives the “beads of rice” bracelet its name. It features small, rounded stainless steel links that resemble grains of rice. The “beads of rice” design was particularly popular in the mid-20th century, notably used in Omega’s Seamaster and Constellation models.

On the outside of the clasp is the raised Omega logo. It is also signed inside the clasp. There are some general light surface markings to the clasp and bracelet, but this is expected on a vintage timepiece. The watch currently fits an 18cm wrist, although there are extra links to extend it to a larger wrist. The Omega n12 “beads of rice” bracelet is adjustable to fit different wrist sizes through link removal/addition and clasp micro-adjustments.

Summary

I must admit this watch is tempting. A vintage Omega Seamaster is high on the list for my collection. Vintage Omega’s are so well made and robust that they still make excellent daily wearers. However, in my mind, the classic Seamaster has the hippocampus logo on the case back. This watch is totally legitimate, and its plain case back is accurate for the date of the watch. However, I want that iconic hippocampus logo. That isn’t to say I would turn this vintage watch down as a gift, and I could see myself wearing it. However, if I am buying my one and only vintage Omega Seamaster, it needs that hippocampus on the case back.

As it turns out, this watch was purchased for me as a gift. It looks fantastic, keeps great time, and the “beads of rice” bracelet is very comfortable. However, I am still on the hunt for that elusive Hippocampus!