The Finnish icebreaker firm Aker Arctic Technology modified the Manhattan for ice conditions. Icebreakers Aker designed following this work included features first included during the Manhattan refit.
Although Canada and the United States are allies in other areas they are in a dispute as to the nature of the Northwest Passage. The USA asserts the passage should be considered an International shipping channel, that vessels of all nations should be able to proceed through without regulation from any nation. Canada asserts that the passages are internal waters and that Canada has the right and responsibility to enforce environmental safety measures there.
The oil interests behind the voyage of the Manhattan pointedly did not file a sailing plan with Canada. Canada stopped short of blocking the vessel, but did escort it with Canadian Coast Guard icebreakers.