The DDX proposed to use permanent-magnet motors (PMMs) within the hull, an approach that was abandoned in favor of a more conventional induction motor. An alternate twin pod arrangement was rejected as the ramifications of pod drives would require too much development and validation cost to the vessel. The PMM was considered to be another technology leap and was the cause of some concern (along with the radar system) from Congress. As part of the design phase, Northrop Grumman had the world's largest permanent magnet motor, designed and fabricated by DRS Technologies. This proposal was dropped when the PMM motor failed to demonstrate that it was ready to be installed in time.