The Russian Admiralty Board had previously licensed the design of the Passaic class from the United States and wished to compare the John Ericsson-designed gun turrets of those ships with the turrets designed by the British inventor Captain Cowper Coles. The board therefore commissioned Mitchell to design a twin-turret monitor based on the Danish ironclad Rolf Krake and to build it in the shipyard that he had modernized for the board in Saint Petersburg, Russia.[1]