His grandfather, also named Joshua Chamberlain, was a colonel in the local militia during the War of 1812 and was court-martialed (but exonerated) for his part in the humiliating Battle of Hampden, which led to the sacking of Bangor and Brewer by British forces.
Hans bedstefar, som også hed Joshua Chamberlain, var oberst i den lokale milits under den Britisk-amerikanske krig (1812) og blev sendt for en krigsret (og frifundet) for sin andel i det ydmygende slaget ved Hampden, som førte til at britiske styrker plyndrede Bangor og Brewer.