Activist investor Carl Icahn acquired about $51 million in the common shares of mortgage financiers Fannie Mae (FNMA.OB) and Freddie Mac (FMCC.OB) from mutual fund manager Fairholme Funds Inc in March, a court filing showed on Tuesday. Icahn, a billionaire investor known for taking big stakes in companies and pushing for management change, bought 6.8 million common shares of Fannie Mae and 5.7 million common shares of Freddie Mac from Fairholme, according to the filing with the U.S. Court of Federal Claims in Washington.