Based on DD433 Gwin (2x quintuple 21" TT) and DD616 Nields (with only 1 set of quintuple 21" TT), this item contains 6 ships of each vessel (12 total), representing typical USN Benson/Gleaves class destroyers as they appeared in 1943. Thirty (30) Bensons were built during 1939–1943 while 66 Gleaves were built (1938–1942).
Though the models are based on the Gleaves class, they don't visually differ much from the Bensons, the later having flat-sided funnels (vs Gleaves' rounded ones).
Selected Online readings:
http://destroyerhistory.org/benson-gleavesclass/
http://www.navypedia.org/ships/usa/usa_torpedo.htm (BENSON, GLEAVES, BRISTOL and LAFFEY entries)
http://en.wikipedia.org/wiki/Benson_class_destroyer
http://en.wikipedia.org/wiki/Gleaves_class_destroyer