Fourth quarter revenue decreased 3.6% versus prior year primarily due to divestitures and COVID-related impacts, mainly for commercial-related sales. Organic revenue was flat for the quarter as 3.7% growth in core U.S. and international businesses, excluding commercial aviation and Public Safety, was offset by the anticipated COVID-related decline. At the segment level, revenue growth was driven by Space and Airborne Systems and Communication Systems, offset by a decline in Aviation Systems primarily due to COVID-related impacts. Funded book-to-bill was 0.93 for the quarter.
Fourth quarter GAAP EPS decreased 48% versus prior year primarily due to charges for the impairment of intangibles, goodwill and other assets related to the commercial aviation business and other COVID-related impacts. These charges and other impacts were partially offset by operational excellence, integration benefits, cost management, a decrease in integration costs and a lower share count. Non-GAAP EPS in