The decision to assign "Sir William Alexander" to the Operation Unison task force was unprecedented in Canadian Coast Guard history as no icebreaker from the service has operated for an extended period of time in southern tropical waters such as the Gulf of Mexico, aside from transiting the Panama Canal to and from British Columbia. On 19 September 2005, it was announced that the three warships were no longer needed in the Gulf of Mexico, given the massive U.S. military response as well as increasing civilian aid flowing into the region. "Sir William Alexander" was exempted from returning to Canada however, as her heavy lift capabilities were considered useful for ongoing repairs to aids to navigation which were destroyed by Hurricane Katrina, and later Hurricane Rita (23 September). On 28 September, the Minister of Fisheries and Oceans announced that "Sir William Alexander" was being retasked from relief efforts and navigation systems repair to assist the National Oceanic and Atmospheric Administration in repairing the damaged network of weather buoys along the Gulf of Mexico, Caribbean Sea, and Atlantic coasts. She returned to CCG Base Dartmouth from Operation Unison on 24 October 2005. "Sir William Alexander" was involved in a fatal towing incident involving the fishing vessel "L'Acadien II" during the 2008 Canadian commercial seal hunt. On 30 September 2014, a Canadian Armed Forces Bell CH-146 Griffon helicopter clipped "Sir William Alexander"s antenna during a training exercise in Mahone Bay. The helicopter was forced to make an emergency landing in Lunenburg, Nova Scotia. In February 2017, "Sir William Alexander" was dispatched to aid the merchant vessel "Thorco Crown", which had caught fire in the Cabot Strait. The engine room fire was extinguished but the merchant was disabled. When a tugboat arrived to take "Thorco Crown" in tow, the tugboat was unable to secure the towline. "Sir William Alexander" then took "Thorco Crown" in tow during the night, transferring the tow to the tugboat in the morning.