The USS Nautilus (SSN-571) was the first vessel to cross the Arctic Basin via the north pole in early August 1958. During this expedition, almost continuous acoustic under-ice thickness profiles were recorded. In August 1970 USS Queenfish (SSN-651) retraced Nautilus' route, yielding the only duplicate transect of under-ice topography across the Arctic Basin. Comparisons of the statistical analysis of the under-ice draft measurements obtained through use of wide-beam and narrow-beam and narrow-beam only acoustic profilers by Nautilus and Queenfish, respectively, along the coincidental route are presented. Geographic areas found to have distinct under-ice characteristics and ice composition are identified. The under-ice statistics of both cruises are considered in relation to reprensentative field observations and modeling results of other reseachers. Principal findings are (1) Nautilus recorded generally more severe ice conditions within the Canada Basin than did Queenfish 12 years later; overall mean drafts were 3.08 and 2.39 m, respectively, (2) the under-ice topography becomes progressively more severe when proceeding from the Canadian to the Eurasian side of the Arctic Basin, (3) the Canada Basin may contain the most moderate under-ice topography and the greatest number of open water and refrozen polynyas and leads within the central Arctic Basin, (4) the Makarov and Amundsen basins and the Arctic mid-ocean ridge may contain some of the most severe under-ice topography within the Arctic Basin and (5) the present study indicates an overall Arctic Basin mean of 3--4% open water/new ice (less than 30 cm) in summer. ¿ American Geophysical Union 1989