1940–1943 Japan 10 Sen — Shōwa Aluminum Type
Shōwa 15–18 · 22 mm wartime aluminum issue · weight reductions documented by year
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The supplied Numista catalogue table separates weight standards within the same dated year. This archive therefore keeps one canonical page per calendar year and documents each listed weight variety inside that page.
Wartime Aluminum 10 Sen
Japan Mint historical material states that the 10 Sen and 5 Sen became non-holed pure-aluminum coins in 1940 and that the coin weight was reduced twice as aluminum became a strategic material. Official Mint Museum specimens document the 1940 1.50 g standard, a 1941 specimen measuring about 1.19 g, and 1943 specimens measuring about 0.98–1.00 g.
Official Sources & Catalogue Cross-check
Japan Mint — Mint Museum Special Exhibition Exhibit Lists
Official Mint Museum records identify the wartime aluminum 10 Sen. The December 2024 list records 1940 specimens at about 22 mm / 1.50 g and 1943 specimens at about 22 mm / 0.98–1.00 g; the August 2024 revised list records a 1941 specimen at 21.98 mm / 1.19 g.
Japan Mint — Mint Club No. 78: History of Holed Coins
Japan Mint explains that the 10 Sen and 5 Sen changed to non-holed pure-aluminum coins in 1940 and that, as aluminum became important for aircraft, coin weight was reduced twice.
Bank of Japan Currency Museum — Wartime Money
The Currency Museum identifies the 1940 aluminum 10 Sen within the wartime shift from nickel and copper toward aluminum and tin under material shortages.
Numista — Japan 10 Sen, Shōwa (N#5438)
Secondary cross-check for year/weight varieties, grouped mintage entries, 22 mm type diameter, 1.49 mm catalogue thickness, reeded edge and Y/JNDA catalogue identifiers. No Numista photographs, valuation table, logo or catalogue prose is reproduced.
Mintage scope caution: the supplied Numista entries use grouped mintage notes across adjacent dates/weight standards. Those secondary figures are preserved exactly as grouped catalogue data and are not relabeled as Japan Mint annual production totals.