A cargo ship loaded with humanitarian aid was headed to Kenya under U.S. Navy escort Wednesday after evading pirates firing grenades and automatic weapons, the second unsuccessful hijacking attempt of an American freighter in a week, officials said. The Liberty Sun's American crew was not injured in the attack but the vessel sustained unspecified damage, owner Liberty Maritime Corp. said in a statement Tuesday night quoted by Associated Press. «We are under attack by pirates, we are being hit by rockets. Also bullets,» crewman Thomas Urbik, 26, wrote his mother in an e-mail Tuesday. «We are barricaded in the engine room and so far no one is hurt. (A) rocket penetrated the bulkhead but the hole is small. Small fire, too, but put out.» The Liberty Sun «conducted evasive maneuvers» to ward off the pirates before help arrived, said U.S. Navy Lt. Nathan Christensen, spokesman for the Bahrain-based 5th Fleet. «That could be anything from zigzagging to speeding up to all kinds of things,» he said. «We've seen in the past that that can be very effective in deterring a pirate attack.» A U.S. Navy destroyer, the USS Bainbridge, responded to the attack but the pirates had departed by the time it arrived some five hours later, Navy Capt. Jack Hanzlik said. After arriving on the scene, the Bainbridge sent «a small security detachment» onboard the Liberty Sun to ensure that its crew of about 20 mariners was safe, Christensen said. Urbik sent a follow-up e-mail to his mother «that said he was safe and they had a naval escort taking them in,» Katy Urbik said.