Excerpted from a NAWCC Bulletin article which appeared in the October 2000 issue. This article does not appear here in its entirety.

The First Japanese Precision Timepieces
A Brief History of the Seiko Marine Chronometer

T. Haruyama (Japan)
(With research assistance from T. Suzuki and F. Eguchi)

Full-sized marine chronometers, equipped with detent escapements and running for 56 hours, were mass-produced by the Japanese company Daini-Seiko-sha during World War II. This watch manufacturing company was part of a group, which also included Hattori, the watch and jewelry retailer, and Seiko-sha, mainly a manufacturer of clocks. Today we know this firm by the names Seiko Instruments Co. Ltd., and Seiko Epson Co.1

The design of the Seiko marine chronometer is an exact copy of the famous Ulysse Nardin chronometers made in Switzerland, right down to the location of the trademark stamp beside the ratchet wheel on the movement backplate. The timepieces and their components were, however, entirely made in Japan.

Prior to the advent of Seiko marine chronometers, Seiko-sha produced five-day running deck clocks and eight-day fusee ships clocks, using good quality lever escapements.2 Although suitable for merchant ships, they were inadequate for use in military navigation. For that purpose, the Imperial Navy used imported marine chronometers by Nardin, Kullberg, etc. The Seiko-sha deck clocks had a rated accuracy of less than plus/minus 12 seconds per day, whereas the naval accuracy standard was plus/minus 1 second per day, during a 20-day test. This was why the navy used full-size imported chronometers for navigation.

The author, with the help of his colleagues, has investigated the short history of Seiko's full-sized marine chronometer, which was produced for only about five years from 1941 to 1945. In this paper I describe its history with quotes from previously secret military documents, interviews with participants of those times, and photographs of a Seiko marine chronometer as well as of an early Nardin chronometer retailed in Japan. These latter timepieces are in the author's collection.

The Origin of the Seiko-sha Full-Sized Marine Chronometer
By about 1938, executives of naval headquarters were feeling the need for a domestically produced accurate marine chronometer. (Then) Naval Commander Ryouichi Sugiyama had taken the leadership of the Naval Navigation Laboratories.3 He approached Kintarou Hattori, the president of Seiko, about producing a domestic chronometer, but Hattori declined, stating that "the marine chronometer business is not profitable at this time."3 Despite repeated attempts to interest Hattori in developing a chronometer escapement, no business contract was made at that time.

By 1938, however, the international political situation was worsening. In 1939, Britain and France declared war on Germany, and in 1941 Japan entered the war. Now Japanese warships desperately needed a good supply of marine chronometers. As a result of this unfortunate situation, Daini-Seiko-sha began in earnest to develop their marine chronometer. They had begun trial manufacturing by 1940, and in that year, a naval engineer reported on the progress of chronometer development.4  In this secret military report, the engineer proposed that an engineering standard should be developed to complete production of accurate timepieces.

Also from the contents of this report it is seen that Daini-Seiko-sha engineers were researching metals and metal processing before a formal request from naval headquarters was made. After formally requesting naval headquarter's support, a team was formed from experts in several fields. In addition to navy personnel, Executive Chief Engineer Yoshinao Fuse brought other engineers from Daini-Seiko-sha, and Professor Hakar Masumoto was invited to the project as an advisor.4 He was from the Imperial University of Tohoku, and was the inventor of coelinvar, an improvement upon elinvar, resulting from the addition of cobalt to the alloy.5 Thus, his experience with temperature-compensating balance springs was invaluable. In 1943 production was moved to Sendai, in the north, for safety from the heavy bombing of Tokyo by B-29 bombers. In the midst of such turbulence, full-scale production of marine chronometers began in 1942.

As stated previously, the Seiko chronometer was based upon the Ulysse Nardin two-day chronometer. The design is identical. Figures 3 (outside appearance), 4 (plaque on outer box), 5 (dial), and 6 (movement) look very much like those of Nardin, in Figures 7 and 8. In fact, many of the parts will fit in either manufacturer's timepiece (albeit with some adaptation).

Seiko-sha never imported any parts, although many were identical to the Nardin parts. All were made in Japan. Jewels were made and supplied by the Ogura Jewelry Co. of Tokyo,6 and most of the rest were made by Daini-Seiko-sha itself.3,6-8

Before beginning mass production, Daini-Seiko-sha engineers studied materials, especially those for use in the balance wheel and helical hairsprings. This was the specialty of Professor Masumoto, who had invented coelinvar, which added cobalt to the iron-nickel-chromium alloy of elinvar. This invention was aimed at further improvements in temperature insensitivity of self-adjusting hairsprings and balances, and had been used successfully in watches. Word has it that Daini-Seiko-sha tried to use coelinvar in the marine chronometer, but this is not a known fact.

The author used an x-ray element analyzer to determine the composition of a Seiko chronometer hairspring, finding that the composition was that of elinvar, not coelinvar. Jiro Sato described the coelinvar as having a higher modulus of elasticity than elinvar, and it is known that even elinvar is very brittle and hard to work with.6 However, they could not manufacture a perfect helical coil-spring using coelinvar6 because coelinvar (then) was too difficult to manipulate to manufacture the complicated helical coil6 (after World War II, Seiko employed coelinvar for their watch coil spring).

Mr. Sato, 6 Daini-Seiko-sha engineer, and former Naval Commander Sugiyama3 state that preparation for mass production began in 1941, and was underway in October 1942. Somewhat less than 600 timepieces were made, including some nearly finished but not used, and supplied for use in the warships of the Imperial Navy of Japan. How good were they?

The Office for Naval Organization was responsible for ordering and approving the chronometers. Daini-Seiko-sha chief engineers also inspected the finished timepieces. Accuracy testing was done by using the pulse rate from Japan radio. The chronometers had a break-circuit for pulse output, (See outlined area in Figure 6.), and this output was compared with the radio pulse. All of the chronometers were adjusted to a daily rate accuracy of plus/minus 1-second / day, and achieved less than 0.5 seconds / day deviation. They met the naval standard (Table 1). Some of the clocks performed even better, with a daily rate deviation of plus/minus 0.1 seconds. Thus, the chronometers were built to a very high level of precision, and were met with great enthusiasm by naval high command.7,8

The short-lived history of the Seiko-sha two-day marine chronometer has been described. Daini-Seiko-sha produced less than 600 of these excellent timepieces during the pressures of World War II. It was an almost exact copy of the Swiss Ulysse Nardin chronometer, successfully built by the engineers of Daini-Seiko-sha and others through an all-out effort to surmount many obstacles. Through their efforts, they achieved a higher level of accuracy than simply copying would have produced, and in the process, undoubtedly sowed the technology seeds that later resulted in the highly accurate post-war Seiko watches. Very few Seiko-sha chronometers survive due to the almost total destruction of the Japanese Navy during World War II.

Grateful thanks go to: Mr. Taro Yasukawa (former Naval Lieutenant) who supplied valuable naval documents; Kyouji Sugiyama (former naval assistant engineer); Masahito Yoshino (Seiko-Epson Co. Ltd.); Ryouchi Sugiyama (former Naval Commander) and Dr. Jerome F. Walker for their great assistance. Special thanks to Doug Cowan, the first vice president of NAWCC, for his help in the editing of the paper.

About the Author
For Professor Dr. T. Haruyama, horology is his hobby, not his profession. He enjoys collecting ships clocks, marine chronometers and pocket watches, especially Japanese chronometers and foreign chronometers retailed in Japan during the Meiji era (1868-1912) and Taisho era (1912-1926).

1. Seiko was established in 1881 by Kintarou Hattori as Hattori Watch and Jeweler in Ginza, Tokyo. In 1892, a manufacturing division was separately established as Seiko-sha. In 1917, Hattori Watch and Jeweler was organized as a company with the two firms. The Seiko brand was first used on watches in 1924. In the course of 1937-1942, the group was separated into three companies: Hattori Watch and Jeweler, Daini-Seiko-sha and Yamato engineering. Daini-Seiko-sha and Yamato engineering mainly produced watches. The Seiko group currently consists of five independent corporations: Seiko Epson (watches, computers, LC, quartz, etc.), Seiko Instruments (watches, electronics devices, measuring instruments, etc.), Seiko (watches and clocks), Seiko clock (clocks) and Seiko precision (watches and clocks). Incidentally, the retail building of Hattori Watch and Jeweler was occupied by GHQ (General Headquarters of US occupation) as the Tokyo PX store after WWII from 1945 to 1952. The present name of the building is Wako, which is owned by Seiko Co. Ltd., and it is a high-class department store.

2. Hattori special instruments catalogue, vol. 10, p. 267, (1936).

3. The author interviewed Ryouichi Sugiyama (former Naval Commander) in 1997.

4. Professor Hakar Masumoto (Imperial University of Tohoku) is well known as an inventor of coelinvar. He was decorated by the First Order of Merit in 1966.

5. Hakar Maumoto, Journal of Metallurgical Society of Japan, 2(4), 141-146 (1938). Hakar Masumoto, Journal of Metallurgical Society of Japan, 8, 513-516 (1944).

6. Jiro Satoh was an engineer of Daini-Seiko-sha and was in charge of development of the full-size marine chronometer during WWII. His remembrance regarding the Seiko marine chronometer was described in Jiro Satoh, Memoirs—history of watch and clock engineering. Eds. by Seiko Co. Ltd. and Japanese managing history laboratory (1981).

7. Seiko-sha Shiwa (History of Seiko Co.), pp. 323-324, Ed. by M. Hirano (1968), Seiko-sha, Tokyo.

8. Taro Yasukawa was a naval engineering officer (Lieutenant) in the Naval Navigation Laboratory. The author interviewed Yasukawa in 1996 and in 1997.

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