In July 2009, "Mahan" participated in Operation Northern Trident, where she met two Royal Australian Navy ships, and , in Halifax, Nova Scotia. The three ships conducted combined exercises at sea and a four-day port visit to New York City, New York. "Mahan" crew members worked with their Australian counterparts in cleaning the Soldiers, Sailors, Airmen, and Marines Center in midtown Manhattan. Receptions were held onboard all three ships while offering tours to the public. Crew members were able to pay their respects by conducting a wreath laying ceremony at the World Trade Center. Several sailors also reenlisted in Times Square and at the World Trade Center site.