For ground-based optical interferometry, the simple specification of high surface quality flat relay mirrors is not the end
of the story for obtaining high quality fringes. The Navy Prototype Optical Interferometer array transports the stellar
radiation from six primary collectors through a 10-reflection vacuum relay system, resulting in six separate combinable
wavefronts. The surface error of each of the 60 relay mirrors is specified to be no greater than 32 nm peak-to-valley for
fabrication purposes. However, once mounted in the 10-element optical train the errors from each mirror do not
necessarily cancel one another, but can add and increase the resultant wavefront distortion for that path. This leads to
fringe contrast reduction, reduced ability to fringe track, and a reduction in the limiting magnitude of observable objects.
Fortunately, the total wavefront distortion for each train can be measured, calibrated, and nullified by using a phaseshifting
interferometer combined with a compliant static deformable mirror and control system. In this paper we
describe a system that mitigates the resultant wavefront distortion.