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.3 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. | 
| Figure 3. The outside appearance of the Daini-Seiko-sha two-day marine chronometer in original outer box. |
Assembly of Seiko-sha Two-Day Marine Chronometers 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 
| Figure 4. Plaque on chronometer outer box. The plaque says “Manufactured by Daini-Seiko-sha, Co. Ltd., Tokyo, Empire of Japan.” |
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. |
