<Tr> <Th_colspan="2"> Iron Brigade </Th> </Tr> <Tr> <Td_colspan="2"> Iron Brigade unit badge, a maltese cross design, showing the Wisconsin, Michigan, and Indiana, Union Army regiments, who were the core of the Brigade, on a historical marker, at Gettysburg National Military Park . </Td> </Tr> <Tr> <Th> Active </Th> <Td> October 1861 - June 1865 </Td> </Tr> <Tr> <Th> Country </Th> <Td> United States </Td> </Tr>

How did the iron brigade get its name