Near the end of the Russian-American Tomography Experiment, November 3 and 4, 1993, the index of magnetic activity (Kp) climbed rapidly from 0 to 7- in a little under 1 day. The quasi-logarithmic Kp index ranges from a low of 0 for very calm conditions to 9 for the most intense magnetic storms. During the course of this magnetic storm the ionospheric response was studied using data collected and analyzed in 28 passes. The results of this intensive study, using contour charts of electron density as well as the three important parameters of the average Chapman profile, the maximum density, the altitude of maximum, and the scale height, are presented. We had dual-frequency receivers set up at four locations on the eastern edge of North America: Block Island, Rhode Island; Hanscom Air Force Base, Massachusetts; Jay, Vermont; and Roberval, Quebec, Canada. Using the dual-frequency (150 and 400 MHz) beacon on the Navy Navigation Satellite System, with a nominal altitude of 1100 km, a tomography pass would typically last about 20 min from horizon to horizon. From a total of 88 passes, 86 passes possessed sufficiently accurate data and have been analyzed using the maximum entropy method, which determines the average vertical profile in the form of an analytical Chapman profile, as well as a set of electron density contours. The Russian tomography experiment, which utilized the same four locations, as well as the incoherent scatter radar results obtained by the Haystack Observatory group, will be discussed at a later date.¿ 1997 American Geophysical Union