Since 2013 North Korean merchant ships, especially the ones known to engage in illegal activities (smuggling weapons and other contraband) have stayed closer to home until they can be replaced or succeed in changing their identity. These ships have been seen operating mainly between North Korea, Iranian, Chinese and Russian ports. These ships can expect to avoid close scrutiny in these countries.
All this circumspection is the result of a mid-2013 incident when a North Korean freighter was inspected and seized last by Panamanian inspectors as the ship arrived to use the Panama Canal. It turned out that the North Korea vessel was not carrying military equipment being sent to North Korea “for repairs” but was Cuban military surplus (stuff the Cubans could not afford to operate and maintain) being sold to North Korea. The illegal cargo of Cuban SA-2 anti-aircraft missile systems and MiG-21 components (including over a dozen jet engines) was buried under a cargo of sugar headed through the Panama Canal. The illegal and undeclared weapons shipment also included some lighter arms. But mostly it was stuff North Korea needed but had a difficult time obtaining (like anti-aircraft missile components and replacement engines for their elderly MiG-21 fleet). The North Korean freighter detained in 2013 had been showing up in Cuba every three of four months. In 2014 this incident led to the UN blacklisting the North Korean shipping company involved (along with all fourteen of its ships). The United States found that more nations were willing to cooperate in finding and tracking North Korean merchant ships engaging in illegal activities. The North Korean merchant shipping fleet consists of about 150 vessels and most are used for smuggling at one time or another.
Often the North Korean ships traveled (in violation of international law) with its tracker turned off. The trips to Cuba were long believed to be some kind of smuggling operation, but since Cuba had little of military value for North Korea, no one looked too closely. At first it was thought that Cuba was trading sugar for repair services (on the missiles and the jet fighters and their engines, which wear out quickly). Soon it was discovered that Cuba was selling their main export (sugar) as well as surplus weapons to North Korea. Cuba is, like North Korea, one of the few communist states to survive the massive collapse of communist countries in the late 1980s and early 1990s. Cuba has been more energetic than North Korea in allowing economic freedom and is economically better off than North Korea but is still short of cash. North Korea and Cuba were in violation of the sanctions against North Korea, although neither is much concerned about international criticism. North Korea has been caught recently buying MiG-21s illegally (from Mongolia) and has been active on the arms black market for over two decades.