Seiko Slim Turtle 7548

In 1978, Seiko introduced the first 150 m diver’s watch with quartz movement in history, the 7548 Slim Turtle, alongside the 600 m and 300 m quartz divers launched the same year. In this guide, we will examine all the known variants of the 7548 divers, produced until the mid-1980s.

Index

• The origins of the Seiko Slim Turtle
• Models for Japan
• Professional 200 m models
• Models for the export market
• Production period
• Military use of the Seiko 7548
• Movement specifications

The origins of the Seiko Slim Turtle

The first Slim Turtle series, based on the quartz caliber 7548, was introduced in 1978 primarily for the export market, and subsequently made available in Japan.
The nickname “Slim Turtle” is due to the design of this model, which is a slimmed-down version of the Seiko Turtle, introduced to the market about two years earlier, in August 1976.

The first models of the 7548 divers for the Japanese Domestic Market (JDM) were launched in May 1979, but the corresponding references for the export market were already available in the 1978 catalog.

In the following announcement sent to authorized Japanese dealers, Seiko detailed the launch of the new models, highlighting the main features of the 7548 and 7549 divers, introduced in Japan in the same month.

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New models of Seiko Quartz Diver 75DVW (300M) and 75DW (150M) watches.
Two new models are added to our reliable line of quartz diving watches.

To our esteemed collection of Seiko diving watches, known for their high quality and reliability, new products are added. The 75DVW is designed for professional divers with specifications for diving up to 300 meters, while the 75DW is intended for recreational diving and freediving, with proven specifications for diving up to 150 meters. These new diving watches incorporate the quartz movement and offer the highest level of resistance to pressure and water. They are the ideal choice for those who practice diving, offering safety and reliability.

Product features:

• High-precision quartz diving watch.
• Guaranteed resistance to pressure and water up to 300 meters (75DVW) and 150 meters (75DW).
• Rounded finish to not damage the skin or wetsuits.
• Robust and comfortable polyurethane strap.

Battery replacement information:

• The battery life is approximately 3 years, both for the 300-meter model and the 150-meter model.
• The time for battery replacement is engraved on the back of the case.
• For the Professional 300 (meters) model, the first battery replacement is free. A coupon for the battery replacement is included in the instruction manual, please hand it to the customers.

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Models for the Japanese market

All the references for the Japanese market were listed in the Seiko catalogs with the GL831 rubber strap. Unlike the export versions, which we will discuss later, the option of a metal bracelet was not available in the catalogs.

To the JDM black, pepsi, and orange models is added the Teal color variant, which has the same case code “7548-700C” as the orange version but appears to be much rarer.
Known examples of the teal version seem to all have serial numbers from December 1984.

Professional 200 m models

Between 1984 and 1985, Seiko produced, exclusively for the domestic Japanese market, two additional references in the 7548 series. These models featured an increased water resistance from 150 to 200 meters, achieved through the introduction of a screw-down ring to secure the crystal.

These transitional models, produced for a brief period, heralded the features of the next generation of Slim Turtle quartz divers equipped with the 7C43 caliber.

The black model (PYH028, 7548-7010) is affectionately nicknamed ‘Brian May’ by enthusiasts because it was a favored accessory of the famous Queen guitarist. He wore it for many years after purchasing it in Japan during Queen’s 1985 tour, which included performances in Tokyo, Nagoya, and Osaka.

Brian May has mentioned on several occasions that he bought the watch during his first trip to Japan; however, this is not possible since the 7548s were not yet in production in 1975, the year of his initial tour there with Queen.

Indeed, it was not until the latter half of 1985 that the Seiko diver began to appear on Brian May’s wrist, shortly after Queen’s tour of Japan in May 1985.

The following frames show the Seiko 7548-7010 on Brian May’s wrist a few months after Queen’s tour in Japan, during the recording of “One Vision”.

Models for the export market

The most noticeable feature distinguishing the 7548s for the export market from those destined for Japan is the presence of the “SQ” logo on the dial.
Below the “SQ” logo, the inscription “Diver’s 150 m” appears instead of “Water 150 m Resist” for the JDM counterparts.
Moreover, while the JDMs were offered in catalogs only with a rubber strap, the export versions often offered a metal bracelet as an alternative, like this Z199S for reference S60577.

Another element that separates the export configurations from the JDMs is the bezel insert of the orange variant, which on the 7548-700C (JDM) features gold lettering, while on the export models 7548-700A and 7548-700H the lettering is silver.

According to some collectors, an export version of the 7548-700C has also been produced, with an “SQ” dial and a black insert with gold lettering, however, I have been unable to find any documentation that confirms the originality of this configuration.

The following table lists all the configurations intended for the export market, confirmed by Seiko documentation that I have been able to consult.

Case code	Reference	Dial code	Color	Band
7548-7000	S60577	700L0349 (7548-700L T)	Black	ZLM08 (rubber strap) Z199S (metal bracelet)
7548-700A	S60579	700L0899 (7548-700L T)	Orange	ZLM08 (rubber strap) Z199S (metal bracelet)
7548-700A	S60595	700L0899 (7548-700L T)	Orange	ZLM08 (rubber strap)
7548-700B	S60581	700L0549 (7548-700L T)	Pepsi	ZLM08 (rubber strap) Z199S (metal bracelet)
7548-700B	S60597	700L0549 (7548-700L T)	Pepsi	ZLM08 (rubber strap)
7548-700F	?	700L0549 (7548-700L T)	Pepsi	ZLM07 (rubber strap) Z199W (metal bracelet)
7548-700H	?	700L0899 (7548-700L T)	Orange	ZLM08 (rubber strap)
7548-7009	S23143	700L0349 (7548-700L T)	Black	ZLM07 (rubber strap) Z199W (metal bracelet)

Production period

The following table aims to provide an approximation of the production period of the 7548 divers, based on the serial numbers associated with the various case codes.

Some important considerations:

• the dates are based on the observation of a limited number of serial numbers, and should be considered as purely indicative;
• although they share some case codes, it can be observed that the production of the first 7548s destined for the export market started a few months earlier than the corresponding JDM versions;
• the rare teal configuration of the 7548-700C (ref. PYH012) seems to have exclusively serial numbers from December 1984.

Code	Oldest serials	Most recent serials
7548-7000	March 1978	February 1985
7548-700A	February 1978	June 1982
7548-700B	January 1978	May 1985
7548-700C	January 1981	December 1984
7548-700F	March 1978	July 1985
7548-700H	March 1978	May 1978
7548-7009	November 1984	May 1985
7548-7010	September 1984	July 1985
7548-701A	August 1984	September 1984

Military use of the Seiko 7548

In the late ’70s, when the first Seiko quartz divers entered the market, they were not only incredibly robust and reliable but also the most accurate diving watches in the world at that time. Given that quartz technology was considered a superior and more desirable alternative to less accurate mechanical watches, it’s no surprise that Seiko divers, including the 7548 Slim Turtle, found widespread use in the military as well as in various professional and sports arenas.

Numerous accounts exist of American navy personnel and other United States army units wearing Seiko 7548s.
One of the most notable examples is the “Seiko Desert Storm”, a 7548-700B worn by General Norman Schwarzkopf, the commander of coalition forces during the First Gulf War.

In February 1999, General Schwarzkopf’s Seiko was sold at a charity auction in New York, complete with a letter confirming its serial number.

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Another Seiko 7548 known for its use in military operations belonged to one of the North Korean divers who landed at Dadaepo, South Korea, in December 1983.

On December 12, 1983, a North Korean commando unit clandestinely landed at Dadaepo Beach, aiming to infiltrate South Korea as part of a broader North Korean plan for espionage and sabotage within South Korean territory. South Korean security forces intercepted the commandos immediately upon their arrival, resulting in a firefight that ended with two spies being captured.

Among the items seized from the North Korean soldiers, two Seiko divers stood out: a 6309-7040 and the 7548-7000, which is visible in this image.

Yet another 7548-7000 was found inside the North Korean spy ship sunk by the Japanese Coast Guard in December 2001, near the island of Amami Ōshima.

Specifications of the 7548 movement

The Seiko 7548, or 7548A, is a precision quartz movement specifically designed for diving watches, thus particularly robust and reliable even for use in extreme environments.
Appreciated both by enthusiasts and professionals for its ease of maintenance, it has the particularity of being designed based on a mechanical caliber, the Seiko 6309, with which it shares some interchangeable parts.

Type	Quartz
Frequency	32.768 Hz
Jewels	5
Battery	U.C.C. 301 (Silver oxide)
Battery life	3 years or more

Technical information and parts list