Further problems hampered the Arctic project after the commencement of drilling in 2012, as Shell dealt with a series of issues that involved air permits, Coast Guard certification of a marine vessel and severe damage to essential oil-spill equipment. Additionally, difficult weather conditions resulted in the delay of drilling during mid-2012 and the already dire situation was exacerbated by the "Kulluk" incident at the end of the year. Royal Dutch Shell had invested nearly US$5 billion by this stage of the project.
What caused the Kulluk incident?