5 Sen - Shōwa Pattern

This is a pattern strike, not a circulation issue — Japan was searching for a cheaper coinage material as military expenditure consumed an ever-greater share of the national budget in the lead-up to and during the Second Sino-Japanese War. Aluminium was the leading candidate precisely because it was being aggressively stockpiled for aircraft production, which made its eventual adoption for coinage a bureaucratic balancing act between the navy, the army, and the mint.

The aluminium 5 sen did reach circulation, but not until 1940. The 1938 date places this piece in the trial phase, before the alloy was formally approved.