actually primary reason was that the B and therefore the N handles better fying off the Midway class carriers. Roosevelt being a prime example (VF84, VF41). the B's were alot more tired with the production run having wraped up around 65 or 66. but what Mako says is true bout war being bad on equipment, thats why Project Beeline came about. bit of trivia, the Marines actually flew B models (not upgraded Ns, straight B) until 1978, and J's until the early 80s. back to the original answer if you check who went from J to N, betcha they either flew off the Midway, Coral Sea or FD Roosevelt ooooorrrrrr they were a Marine unit and the Navy took their Js away!!!