Shop By Category

A Quick Guide To Everything You Need To Know About The Seiko Baby Tuna

Seiko Baby Tuna Banner

The Seiko Prospex Automatic Diver, fondly known as the ‘Baby Tuna,’ is a more affordable offshoot of the professionally crafted MarineMaster Tuna. Designed with the same commitment to quality, the Seiko Baby Tuna offers an excellent balance of professional specifications and value for money.

Seiko Prospex Baby Tuna Limited Model SBDY055 Made in Japan

In this article, we give you a brief overview, diving into the fascinating history behind this series, showcasing two exemplary models, and emphasising their specifications and price points.

FAQs about Seiko Baby Tuna

If you are looking for some quick answers on the Seiko Baby Tuna, we have you covered with four of the most frequent questions on the model:

When did the first Seiko Tuna make its debut?

After an extensive development period of seven years, the inaugural Tuna model, Reference 6159-7010, was launched in 1975.

What exactly is the Seiko Baby Tuna?

The Seiko Baby Tuna is a nickname for the Seiko Prospex Automatic Diver, a more accessible version of the highly professional MarineMaster Tuna.

Does the Baby Tuna wear big on my wrist?

Contrary to typical divers, Tuna watches give the impression of being smaller than their actual case size. This can be attributed to the almost invisible lugs, which lead to a highly rounded case shape.

Diversity among Seiko Tuna models:

Since the first Tuna model in 1975, Seiko has introduced an array of Tuna variations, exhibiting numerous distinctions within the same design family. The options seem endless, with differences in case dimensions, colour schemes, materials, straps, water resistance, movements, and price points.

What’s the origin of the name Seiko Baby Tuna?

The unique design and Seiko’s inventive spirit led to the nickname “Tuna Can,” which reflects the watch’s shape and has endeared it to fans for decades.

The Tuna moniker was first coined by Seiko enthusiasts on an online forum during the early days of the internet. The nickname has less to do with any similarities between the fish and the watches themselves and more to do with the case design resembling an open can of tuna

The Tuna’s Impressive Yet Overlooked History

The Seiko Tuna Dive series was introduced in 1975 and has been improved consistently. Seiko’s dive watch journey began in 1965. Still, everything changed when a professional saturation diver from Kure City, Japan, contacted the company. His letter highlighted issues with Seiko divers’ watches retaining Helium gas, causing the inner pressure to increase and the crystal to pop, ultimately destroying the timepiece.

As a result, the now legendary Ikuo Tokunaga Sama and his team of engineers set out to create the ultimate professional dive watch, giving birth to the iconic Tuna design. Its shrouded case design was Seiko’s answer to the Helium Escape Valve, making for an almost impenetrable watch.

Ikuo Tokunaga Sama - Featured in -Everything You Need To Know About The Seiko Baby Tuna
Ikuo Tokunaga Sama – Image: Source

Seiko’s Unwavering Focus on Dive Watch Excellence

Seiko’s unwavering focus on dive watches is evident in their commitment to designing the first-ever dive watch. The company’s dive watches are designed for rigorous use by divers, with specific features tailored to perform optimally in underwater environments.

The Tuna watch was the first dive watch to feature a top-loading crystal with an L-shaped gasket and titanium construction. With few watches on the market suitable for saturation divers, the Tuna is a great option for this very niche market.

Decades of Research and Development

The Baby Tuna’s design and features reflect Seiko’s dedication to innovation and excellence. The brand has consistently pushed the boundaries of dive watch capabilities since its first dive watch in 1965. Investing in a Baby Tuna means investing in Seiko’s rich history and expertise in dive watch design.

Seiko 1965 Original Dive Watch
Seiko 1965 First Divers Watch – Image: Source

Continuing the Legacy: The Baby Tuna

The Baby Tuna retains its predecessors’ charm and quality construction while offering a more wearable 46.5mm size, this paired up with the almost invisible lugs makes for a very comfortable watch

We have chosen the following two models as our pick of two Seiko Baby Tuna examples:

Seiko Prospex Baby Tuna Limited SBDY055, Made in Japan with Blue Gradient Dial

Seiko Prospex Baby Tuna Limited SBDY053 Made in Japan with Frost Blue Dial

These are both rugged and reliable timepieces featuring a stainless steel protective shroud that increases the case diameter. The screw-down crown is offset at the four o’clock position. The watches are powered by the 24-jewel Seiko calibre 4R36 automatic (self-winding) movement, which are both hand-winding and hackable.

Seiko Baby Tuna Lume
Seiko Baby Tuna Lume

The Baby Tuna boasts the robust Seiko LumiBrite luminescent material on its hands and markers, giving it the same brilliant glowing properties as the Seiko Monster. It also features a 22mm lug width, a slightly domed Hardlex mineral crystal, a concave uni-directional rotating dive bezel, a Seiko stainless steel bracelet with a dual push-button deployant clasp (and diver extension), a solid screw-in case back, and 200-meter water resistance.

The Evolution of Seiko Dive Watches

As mentioned Seiko’s exceptional dive watches began in 1965 with Reference 6217 (or 62-MAS). Over the years, they introduced groundbreaking models like the Reference 6159-7001 in 1968, paving the way for today’s successful Seiko Marine Master divers.

After seven years of development, Seiko released the first Tuna, Reference 6159-7010, specifically designed for saturation diving. The Golden Tuna (Reference 7549-7000) followed, and the Baby Tuna (Reference 7459-7010) eventually joined the Tuna family.


In summary, the Seiko Baby Tuna stands as a testament to Seiko’s rich history in creating exceptional dive watches. These timepieces provide an accessible, durable, and dependable option. Whether you’re a seasoned professional diver or a casual watch enthusiast, the Baby Tuna is a remarkable choice that is sure to impress.

While the Seiko Baby Tuna’s rugged aesthetic and sturdy case may not appeal to everyone, it has cultivated a dedicated fan base who admire its bold design and striking presence. These watches demonstrate Seiko’s unwavering commitment to meeting the needs of even the most niche markets, as the brand continuously strives for excellence and remains attuned to customer feedback.

As a proud member of Seiko’s esteemed Prospex collection, the Baby Tuna embodies the brand’s dedication to expert craftsmanship and watchmaking excellence. The versatile Prospex series boasts an impressive array of timepieces tailored for sea, land, and sky enthusiasts alike, highlighting Seiko’s limitless ingenuity and technological thirst.

If you are interested in purchasing the Seiko Baby Tuna we recommend checking out trusted online retailers or authorized Seiko dealers to ensure you buy an authentic and genuine product. Remember to look for the Prospex logo as a guarantee of quality and performance.

For those of you wanting to read up further on the in depth story of one of our favourite brands I highly recommend: Seiko takes on the World: Japanese Dragon vs Swiss Monopoly to check out the rest of the blog you can do so right here.