1940–1943 Japan 5 Sen — Shōwa Aluminum Type
Shōwa 15–18 · Golden Kite design · 19 mm wartime aluminum issue
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Wartime Aluminum 5 Sen
Japan Mint historical material states that the 10 Sen and 5 Sen changed to pure-aluminum coinage in 1940 and that both denominations were reduced in weight in 1941 and again in 1943. The Bank of Japan Currency Museum specification table records the 5 Sen standards as 19.0 mm / 1.2 g from 1940, 19.0 mm / 1.0 g from 1941 and 19.0 mm / 0.8 g from 1943.
Official Sources & Catalogue Cross-check
Japan Mint — 150 Years of History
Japan Mint records that the 10 Sen and 5 Sen were changed to pure-aluminum coinage in 1940. As aluminum became increasingly important for aircraft, the weights of both denominations were reduced in 1941 and again in 1943.
Japan Mint — Mint Museum Special Exhibition Exhibit List
The official Mint Museum exhibit list records 1943 5 Sen aluminum specimens at approximately 19.01–19.08 mm in diameter and 0.80 g in weight, supporting the final wartime reduced standard.
Bank of Japan Currency Museum — Coins Since the Meiji Era
The Currency Museum's official reference table identifies the pure-aluminum 5 Sen standards as 19.0 mm / 1.2 g from 1940, 19.0 mm / 1.0 g from 1941, and 19.0 mm / 0.8 g from 1943, with a reeded edge.
Numista — Japan 5 Sen, Shōwa (N#9225)
Secondary cross-check for dated varieties, grouped mintage entries, catalogue thickness, design description and Y/JNDA identifiers. No Numista photograph, valuation table, logo or copyrighted catalogue illustration is reproduced.
Mintage scope caution: the supplied Numista N#9225 table leaves some adjacent-year entries blank while placing quantities on the 1940, 1941 reduced-standard and 1943 rows. Those figures are preserved as secondary catalogue data; no arithmetic split and no unsupported official annual attribution is invented.