However 15 - inch guns had been successfully cast using the techniques developed by Thomas Jackson Rodman .
Dahlgren 's efforts with the XIII - inch shell gun were unsatisfactory and it was not clear that he could solid cast a 15 - inch gun .
15 - inch guns had been successfully cast using the techniques developed by Thomas Jackson Rodman .
Dahlgren 's efforts with the XIII - inch shell gun were unsatisfactory and it was not clear that he could solid cast a 15 - inch gun .