1938–1940 Japan 1 Sen — Shōwa Yatagarasu Aluminum Type
Shōwa 13–15 · pure aluminum · official standard 17.5 mm · 0.9 g
Select a Year
Each calendar year has an independent archive page. The 1939 page documents both Numista date-character variants without inventing separate variant mintages.
Yatagarasu Aluminum 1 Sen
Japan Mint official history states that difficulty obtaining copper caused the 1 Sen brass coin to be replaced by aluminum soon after the Temporary Currency Act, marking the first Japanese use of pure aluminum as coinage material. Japan Mint Museum records the Yatagarasu aluminum 1 Sen production period as 1938 through 1940.
Official Sources & Catalogue Cross-check
Japan Mint — Mint Museum Special Exhibition Exhibit List
Official Japan Mint Museum exhibit records identify the Yatagarasu 1 Sen aluminum type and give its production period as 1938–1940. Measured museum specimens for the type are recorded at approximately 17.4–17.5 mm and 0.90 g.
Japan Mint — 150 Years of History
Japan Mint explains that difficulty obtaining copper led to the 1 Sen brass coin being replaced by an aluminum coin soon after the Temporary Currency Act. It identifies this as Japan's first adoption of pure aluminum as coinage material and gives the 1938 1 Sen aluminum standard as 17.5 mm and 0.9 g.
Bank of Japan Currency Museum — Coins Since the Meiji Era
The Bank of Japan Currency Museum lists the wartime 1 Sen aluminum coin as aluminum 100%, 17.5 mm diameter and 0.9 g weight, with the Yatagarasu design and issue beginning in 1938.
Numista — Japan 1 Sen, Shōwa (N#8949)
Secondary cross-check for 1938–1940 dating, catalogue diameter and thickness, annual mintage figures, inscriptions, catalogue identifiers and the 1939 Type A / Type B date-character distinction. No Numista photograph, valuation table, logo or catalogue prose is reproduced.
Specification rule: official 17.5 mm / 0.9 g values are primary. Numista's 17.6 mm diameter and 1.70 mm thickness are retained only as secondary catalogue values. Annual mintage figures remain explicitly attributed to Numista because an official year-by-year table for this historical type was not located in the consulted sources.