Hi Guest, Yes, capitalize the name of any specific unit, and unless anyone else here comes up with an official military method, I personally would spell out the low numbers following the same style guideline as for other numerical writing: that is, 'one' through 'twelve' are written out, and beginning with '13', use the figures (the cut-off point varies slightly with the style guide). So, 'Twelfth Heavy Artillery' and '13th Regiment'.
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