From: Planning the end of the world, well out to 2023!
The game spells it BOTANKO.
It could be either the 1st, 2nd and 3rd, all armed with the 240mm Type 45 howitzer.
or the 2,191-man Mutanchioang and 1,548-man Tungning Heavy Artillery Regiments, also with 240mm howitzers.
Ness, Leland. Rikugun: Guide to Japanese Ground Forces 1937-1945: Volume 1: Tactical Organization of Imperial Japanese Army & Navy Ground Forces . Helion and Company. Kindle Edition.
I'd go with Mutanchioang(probably japanese spelling) as wiki says the following
Mudanjiang (Chinese: 牡丹江; Manchu: Mudan bira) is a prefecture-level city in the southeast part of Heilongjiang province, People's Republic of China. It was called Botankou under Japanese occupation
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