A.M. Best Co. has affirmed the financial strength rating (FSR) of A (Excellent) and issuer credit ratings (ICR) of “a” of Atlantic Specialty Insurance Company (New York, NY) and its three reinsured affiliates, collectively referred to as OneBeacon Insurance Group (OneBeacon). At the same time, A.M. Best has affirmed the ICRs of “bbb” and debt ratings of OneBeacon’s publicly traded parent, OneBeacon Insurance Group, Ltd. (OneBeacon Ltd.) (Hamilton, Bermuda)(NYSE:OB), and its intermediate holding company, OneBeacon U.S. Holdings, Inc. (OneBeacon U.S.). Concurrently, A.M. Best has affirmed the ICR of “bbb” of the group’s ultimate parent, White Mountains Insurance Group, Ltd. (White Mountains) (Hamilton, Bermuda)(NYSE:WTM). The outlook for all the above ratings is stable. Additionally, certain indirect subsidiaries of OneBeacon Ltd. (containing the group’s run-off business) were placed under review in October 2012, as a result of their planned sale to Armour Group Holdings Limited (Amour). Certain of these companies remain under review with negative implications pending completion of the sale. The ratings of the remaining companies have been withdrawn, as they have been merged into affiliates. (Please see below for a detailed listing of the companies and ratings.) The affirmation of OneBeacon's ratings reflects its sound level of risk-adjusted capitalization and strong earnings derived from its generally profitable underwriting performance and solid investment earnings. The ratings also consider the financial flexibility of OneBeacon U.S. and OneBeacon Ltd. These positive rating factors are partially offset by the historical adverse development of the loss reserves of the run-off business, the payment of significant shareholder dividends, which have constrained growth in surplus, and the elevated level of equity investments, which while well-managed, adds volatility to the group’s earnings and balance sheet. In addition, A.M. Best remains somewhat concerned by the risk inherent in pursuing a more concentrated business strategy following the sale of OneBeacon’s personal lines and standard commercial lines businesses. However, A.M. Best’s concern with the less-diversified strategy is significantly offset by the profitability of OneBeacon’s specialty business.