 In the DVD documentary The Thunderbirds Companion , Anderson explained how a rise in filming costs had made overseas distribution revenue even more important and essentially caused Thunderbirds to be made " as an American show " . During the character development and voice casting process , the Andersons ' main priority was to ensure that the series had transatlantic appeal , thus increasing the chances of winning an American network deal and the higher audience figures that this market had to offer . <unk> were <unk> in American English and printed on US @-@ style <unk> @-@ size paper . 
