The details of the work involved in the substitution by the ship's force of the Arkansas, of an electric motor for the wrecked starboard main circulating pump, have been here assembled for the reason that, while they demonstrate nothing new, at the same time they involve certain principles of electrical and mechanical engineering in a most instructive manner. In addition this work has emphasized one fundamental principle, namely, that all apparatus delivered to the service should be as near the commercial standard as possible, and that service operation should conform to the commercial standard, so that in emergency the resources of the whole country, rather than a limited reserve, are available for use. This point was demonstrated in the attempt to obtain a suitable motor from shore. Whereas most commercial motors are built for a voltage of 220-230, the navy power circuits carry 125 volts, so that it was impossible to obtain on short notice a motor fulfilling the requirements. Instead it became necessary to adapt one of the ship's motors to the service, and take extraordinary precautions to maintain it in operation.