The interesting aspect of the Fantastic Voyage animated series is it's history....originally 20th Century-Fox was considering doing a live TV series based on the film. Veteran TV writers William Reed Woodfield and Allan Balter ('Voyage to the Bottom of the Sea', 'Lost in Space', 'Mission Impossible') came up with the series version in 1967, but the series idea was shelved, partially due to the untimely death of writer Balter in a plane crash.
20th Century-Fox had given the rights to another of their sci-fi action-adventure films, 'Journey to the Center of the Earth' to Filmation the previous year and was warmly received. So Fox decided to go with the less expensive route of animation rather than live-action with the added expensive of model work and set building (ala Land of the Giants).
In is also interesting to note that Filmation later did a special animated version of 'Lost in Space'....rumors abounded in the mid-70's that if the LIS cartoon had been picked up by the ABC network, then Filmation was poised to do animated versions of the other Iriwn Allen series, 'Time Tunnel', 'Land of the Giants', and 'Voyage to the Bottom of the Sea'.