From July 2004 to July 2005, "Northumberland" underwent an extensive refit at Number 1 Dock (Inner) at Babcock's dockyard in Rosyth, her first refit since build. This refit saw her equipped with an updated suite of weapons and sensors (e.g. a modified 4.5" Gun and the latest Low Frequency Active Sonar) and of propulsion and mechanical systems. Improvements were also made to the living quarters and a state of the art galley to feed the Ship's Company. Also replaced were corroded areas of the flight deck, improvements were made to the lighting system used during night landings and a new helicopter handling system to move a 13-ton Merlin helicopter safely in and out of the hangar installed. (Although the Type 23 was originally designed to operate the Merlin, "Northumberland" had previously only hosted the much smaller Lynx.) The combination of 2087 LFAS and Merlin ASW helicopter has subsequently proved highly effective and the class is widely regarded as the most capable anti-submarine frigate afloat.