 Production of Thunderbirds ended in August 1966 with the completion of the sixth episode of Series Two . In February that year , it had been reported that Grade had been unable to sell the series in the United States due to disagreements over <unk> . In July , he cancelled Thunderbirds after failing in his second attempt to secure an American buyer . The three major US networks of the time – NBC , CBS and ABC – had all bid for the series , with Grade repeatedly increasing the price . When NBC withdrew its offer , the other two immediately followed . 
