https://www.militarysunhelmets.com/2016/part-i-1887-1921
https://www.militarysunhelmets.com/2016/the-evolution-of-the-japanese-imperial-army-sun-helmet-part-ii-1921-30
https://www.militarysunhelmets.com/2016/the-evolution-of-the-japanese-imperial-army-sun-helmet-part-iii-1930-39
https://www.militarysunhelmets.com/2016/the-evolution-of-the-japanese-imperial-army-sun-helmet-part-iv-1939-41