Abstract : As an element in the Coast Guard's compliance strategy for decreasing greenhouse gases (GHG), and increasing the use of alternative fuels, the USCG Research & Development Center tested 100 percent biodiesel (B100), a renewable alternative diesel fuel, on a USCG 49' Buoy Utility Stern Loading (BUSL). B100 derived from Waste Vegetable Oil (WVO) was obtained from a local supplier, and fuel quality was monitored throughout the test. Prior to operational testing, a materials audit for compatibility with B100 was performed on the fuel-wetted components on the three diesel engines (two main propulsion engines and one generator), and incompatible components were replaced with suitable substitutes. Break-in testing was conducted before the start of operational testing to ensure no B100 compatibility issues remained. Engine exhaust emissions were not measured, but were estimated though an analysis of previous studies on similar engines. Operational testing was conducted over a one-year period starting in March 2013. During this time, the BUSL carried out typical missions in its normal eastern Long Island Sound operating area. Engine performance data were collected and analyzed, along with crew observations of boat performance and maintenance. Details of the testing, and the conclusions and recommendations are included in the report.