NEW HAVEN — In the midst of the Cold War, a U.S. Coast Guard ship dedicated by President Harry Truman embarked on a novel mission. The 338-foot ship had only small arms and giant balloons to hold up the antennas vital to its task. The Coast Guard cutter Courier arrived at the island of Rhodes in Greece in 1952 and stayed until 1964, setting a record for longest deployment overseas. Under an initiative code-named Operation Vagabond, the ship served as a floating and mobile radio relay station, using its powerful transmitter to broadcast Voice of America programs into parts of the Soviet Union, communist bloc countries and the Middle East.Soviet attempts to jam the broadcasts were a constant challenge. “There was a thrill to it because you were playing a game and it was your skill against theirs,” said Robert James, an electronics technician on the ship during the early 1960s. “There was a fun aspect to it because you knew you were participating in the Cold War even though you weren’t shooting guns or anything like that.”The U.S. Coast Guard Museum at the U.S. Coast Guard Academy in New London is marking the 50th anniversary of the end of the mission with an exhibit beginning Thursday. The exhibit includes a model of the ship, along with photos and artifacts of the cutter and the community of Rhodes.The Courier relayed broadcasts from the United States in more than a dozen languages seven days per week with a signal three times more powerful than a land-based signal and the most powerful transmitter ever installed on board a ship. It was the only mobile transmitter in the Voice of America’s network of overseas relay bases.While there had been earlier experiments during World War II to broadcast from ships, the Courier became the first lengthy ship-borne transmitter of Voice of America programming, said Robert Hickman, an organizer of the exhibit whose father ran electronics on the ship.The Courier enabled Voice of America to quickly build up an audience because land-based installations took longer to establish, said George Jacobs, who served as assistant chief engineer for Voice of America.The programming, designed to counter Soviet propaganda, included news, as well as music ranging from jazz to folk.James was shocked one day when they played his native Pennsylvania Dutch.“They wanted to let other people know that there were so many different groups of people that were kind of getting along in the U.S. and living pretty happily,” said James, a 76-year-old Alaska resident.The Courier initially used helium balloons to hold up antennas, but the balloons’ cables snapped in heavy winds and scared people and cattle in nearby Turkey. Voice of America abandoned that approach and designed an antenna that could be supported between the two masts of the ship.A communist newspaper published an article stating that a submarine had been sent to sink the Courier, but the threat never materialized. Technicians found ways to overcome the jamming, such as by transmitting the same program on several different frequencies.“You could tell when the jams came in,” said David Newell, an electronic technician on the ship. “It sounded like a coffee grinder.”The strategy worked. Years later, Newell and his wife Marcia visited the Voice of America in Washington and found short letters written on toilet or tissue paper from listeners describing how the broadcasts gave them hope.“To read those letters it brought tears to our eyes,” Marcia Newell said.