Simplify the following text for a Grade 15 native English-speaking person.
Original: Besides being the first cruise ship ever built specifically to ply the frigid waters of the Antarctic Ocean , the Explorer became the first ever to sink there when it struck an unidentified submerged object , possibly ice , on November 23 2007 which caused a 10 by 4 inch ( 25 Ã -- 10 cm ) gash in the hull .
Simplified: The Explorer was the first cruise ship designed specifically to sail the icy waters of the Antarctic Ocean , and the first to sink there when she struck an unidentified submerged object on November 23 , 2007 , reported to be ice , which caused a 10 by 4 inch ( 25 Ã -- 10 cm ) gash in the hull .