We are also pleased that David McElroy will be replacing Mark as the Chief Executive Officer of our Insurance group and that Michael Murphy will become President of our U.S. underwriting operations and will also be our Chief Underwriting Officer for the Worldwide Insurance Group.
I have tremendous confidence in these individuals and our entire senior management team in both our Insurance and Reinsurance group. Accordingly, we are well positioned at Arch to move our business forward based on the improvement we see in the market opportunities and market conditions.
All of these appointments, once again, demonstrate the deep bench we have built at Arch and our ability to promote first from within and to give all of our people the ability to grow professionally over time.
Now let me turn back to our quarterly results. On an operating basis, we earned $1.2 per share, which on an annualized basis represents a 12.3% return on equity. Our reported underwriting performance was excellent, with a combined ratio of 87.2, while our investment performance for the quarter, including the effects of foreign exchange, was satisfactory, with a total return of 63 basis points for the quarter.Cash flow was $252 million, an increase of $30 million over a year ago and $100 million over the past quarter. Our book value per common share was $34.45, a 3.4% increase from March 31, 2012, and a 12.2% increase from a year ago. We also had very strong revenue increases for the quarter, which I will comment on in a few minutes. The market environment continues to show improvement across the board in our U.S. Insurance business, where we have the strongest statistics both by volume and granularity. Rates increased on a weighted average by approximately 4%, which is 1% better than last quarter and slightly above our weighted averages loss trends.