Rìběnrén céng bǎ gān hǎiyíng zuòwéi zhànshí de biànxié guāngyuán.
Japanese forces once used dried sea fireflies as a portable wartime light source.
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During WWII the Japanese military collected and dried 海萤 (umihotaru) because crushing and wetting them produces just enough blue light to read a map by - no matches required.
