With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Cambodia have minority groups.
text_B: The Mackerel-class submarines were a pair of experimental prototype submarines built just prior to World War II and launched in 1940 and 1941 .. World War II. World War II. The two submarines were similar in size and capability to the S-class submarines built at the end of World War I , and had been ordered to test the feasibility of using mass production techniques to build small submarines .. S-class submarines. United States S-class submarine. World War I. World War I. Until at least 1940 it was thought that mass production of fleet submarines would be impractical , and in any case small submarines could provide area defense for submarine bases .. submarine. submarine. Once it became apparent that there would be sufficient production of the more capable s , interest in the design waned and no additional small submarines were ordered .. Submarine production standardized during the war on the Gato class and its successors , the and submarines .. In some references , the Mackerels are called the `` M class '' .
not_related.