WASHINGTON, D.C. (AP).- In an era of modern airplanes it’s easy to forget how much the United States depends on merchant ships — and always has. A new set of postage stamps is honoring their tradition. On sale starting Thursday, the four Forever stamps are being released in ceremonies at Kings Point, N.Y., home of the U.S. Merchant Marine Academy. “The men and women who built and sailed the ships depicted in these four postal stamps have buoyed our prosperity, liberty and way of life,” David T. Matsuda, head of the U.S. Maritime Administration, said in a statement. “Their sacrifice is worthy of remembrance, as they continue to be an integral part of America’s economy and national security.” Featured on the stamps are: A clipper ship, with art based on an undated Frank Vining Smith lithograph of the famous clipper Sovereign of the Seas, which launched in 1852. Noted for their streamlined shape and square-rigged sails, these vessels set numerous speed records. An auxiliary