The Baltimore is the lead ship of the class of heavy cruisers unrestricted by pre-war Naval Treaties. The first 4 ships (CA68 Baltimore, CA69 Boston, CA70 Canberra and CA71 Quincy) were laid down in 1941 and commissioned 1943. They can be differentiated from the later class-ships by the characteristics of their stern: flat transom, with two aircraft handling cranes and a quad 40mm tub ofset to port.
http://en.wikipedia.org/wiki/USS_Baltimore_(CA-68)http://en.wikipedia.org/wiki/Baltimore_class_cruiser