On December 17, 1972, Singapore issued another set of 3 "Shipping" stamps (SG #s 185-7), and also a souvenir sheet (SG # MS 188) containing the 3 values. The 15c stamp depicts "Neptune Ruby", Singapore's first domestically built container ship.
From the straits times website, " Built by Jurong Shipyard, Neptune Ruby
was the first ocean-going vessel built by Singapore. Prior to that, Singapore had only constructed small coastal and patrol vessels."