OSLO (Reuters) -Norway said on Sunday it had chosen Britain as its strategic partner for the acquisition of new frigates in its biggest ever military investment, in a deal worth some 10 billion pounds ($13.51 billion) to boost the Nordic country's maritime defence. Germany, France, Britain and the United States had offered rival frigate designs in competition. "The frigates are an essential part of our defence because they are key to defend our sovereignty," Prime Minister Jonas Gahr Stoere told