The ice-class mobile offshore drilling unit (MODU) Kulluk, owned by Shell Offshore, Inc., and operated by Noble Drilling, grounded in heavy weather near Ocean Bay on the eastern coast of Sitkalidak Island off Kodiak Island, Alaska, about 2040 local time on December 31, 2012. The Kulluk, under tow by the ice-class anchor-handling tow supply vessel Aiviq, departed Captains Bay near Unalaska, Alaska, 10 days earlier for the Seattle, Washington, area for maintenance and repairs. Four crewmembers on the Aiviq sustained minor injuries as a result of the accident.

​We ​determined that the probable cause of the grounding of the mobile offshore drilling unit Kulluk was Shell’s inadequate assessment of the risk for its planned tow of the Kulluk, resulting in implementation of a tow plan insufficient to mitigate that risk.