As part of the U.S. Maritime Administration (MARAD) marine application of alternative fuel initiative, the U.S. Navy provided neat hydrotreated renewable diesel (HRD), derived from the hydroprocessing of algal oils, for operational and exhaust emission testing onboard the T/S STATE OF MICHIGAN. This vessel has diesel-electric propulsion with four caterpillar D-398 compression ignition engines; one of these ship service diesel engines was selected as the test engine. The diesel generator sets power both the propulsion motors propelling the ship and provide the electrical power for the hotel loads of the ship. Ultra-low sulfur diesel (ULSD) was blended with the neat HRD fuel in a 50/50-by-volume blend and tested for over 440 hours on the vessel. Exhaust emissions testing was performed while underway on Lake Michigan using the baseline ULSD assessed earlier. A similar profile was run using the blended test fuel. Emission testing was conducted using the ISO 8178 (D2) test cycle. When emissions testing was completed a series of underway and pierside test runs were conducted to accumulate the remaining engine hours, After all testing, the engine conditions were assessed again using a combination of visual inspection and oil analysis. The remainder of the test fuel will be used to conduct a long-term stability test. The setup, test, and results of this testing, currently underway, are reported here with a discussion of MARAD’s alternative fuels test initiative.