From the CIA library:
Merchant marine may be defined as all ships engaged in the carriage of goods; or all commercial vessels (as opposed to all nonmilitary ships), which excludes tugs, fishing vessels, offshore oil rigs, etc. This entry contains information in four fields – total, ships by type, foreign-owned, and registered in other countries.
Total includes the number of ships (1,000 GRT or over), total DWT for those ships, and total GRT for those ships. DWT or dead weight tonnage is the total weight of cargo, plus bunkers, stores, etc., that a ship can carry when immersed to the appropriate load line. GRT or gross register tonnage is a figure obtained by measuring the entire sheltered volume of a ship available for cargo and passengers and converting it to tons on the basis of 100 cubic feet per ton; there is no stable relationship between GRT and DWT.
Ships by type includes a listing of barge carriers, bulk cargo ships, cargo ships, chemical tankers, combination bulk carriers, combination ore/oil carriers, container ships, liquefied gas tankers, livestock carriers, multifunctional large-load carriers, petroleum tankers, passenger ships, passenger/cargo ships, railcar carriers, refrigerated cargo ships, roll-on/roll-off cargo ships, short-sea passenger ships, specialized tankers, and vehicle carriers.
Foreign-owned are ships that fly the flag of one country but belong to owners in another.
Registered in other countries are ships that belong to owners in one country but fly the flag of another.
North Korea
Total: 167
By type: bulk carrier 11, cargo 121, carrier 1, chemical tanker 4, container 3, passenger/cargo 3, petroleum tanker 19, refrigerated cargo 4, roll on/roll off 1
Foreign-owned: 19 (Egypt 1, Greece 1, Lebanon 1, Lithuania 1, Romania 4, Syria 1, UAE 8, Yemen 2)
Registered in other countries: 2 (Mongolia 1, Panama 1) (2008)South Korea
Total: 812
By type: bulk carrier 212, cargo 226, carrier 2, chemical tanker 133, container 80, liquefied gas 33, passenger 5, passenger/cargo 26, petroleum tanker 61, refrigerated cargo 16, roll on/roll off 9, specialized tanker 4, vehicle carrier 5
Foreign-owned: 31 (China 1, Japan 20, Norway 2, UK 1, US 7)
Registered in other countries: 363 (Belize 1, Cambodia 22, China 1, Cyprus 1, Honduras 6, Hong Kong 3, Kiribati 2, Liberia 3, Malta 2, Marshall Islands 10, Mongolia 1, Netherlands 1, Panama 303, Russia 1, Singapore 3, Tuvalu 1, unknown 2) (2008)
See a thorough study the the DPRK’s merchant fleet here.
