interest for more than a few seconds per shot. After viewing the finished pilot, "Trapped in the Sky", Lew Grade was so impressed with the series that he instructed Anderson to extend the length of each episode from 25 to 50 minutes – enough to fill an hour-long commercial timeslot. He also increased the budget per episode from £25,000 to £38,000. As a result, Thunderbirds became not only APF's longest and highest-budgeted production, but also one of the most expensive TV series ever made up to that point. The total budget for the 26-episode Series One was approximately £1 million (about £ million in ). The production, which had been shooting two 25-minute episodes every two weeks, faced great challenges transitioning to the new format: nine episodes had already been fully or partly filmed, scripts for ten more had been written, and major rewrites would be needed to satisfy the longer running time. Anderson lamented: "Our time-scale was far too drawn out. ITC's New York office insisted that they should have one show a fortnight ... Everything had to move at twice the speed." APF spent over seven months extending the existing episodes and filmed the new 50-minute format at a rate of two episodes every four weeks. Tony Barwick, who had impressed Pattillo and the Andersons with an unsubmitted script that he had written for Danger Man, was recruited to assist in writing subplots and filler material. He found that the longer format created opportunities to strengthen the characterisation. Science fiction writer John Peel suggests that "small character touches" make the puppet cast of Thunderbirds "much more rounded" than those of earlier APF series. He compares the writing favourably to that of live-action drama. The new footage proved useful during the development of the first series finale, "Security Hazard": since the previous two episodes ("Attack of the Alligators!" and "The Cham-Cham") had overspent their budgets, Pattillo devised a flashback-dominated clip show containing only 17 minutes of new material to reduce costs. Filming of Series One was completed in December 1965. A second series was also commissioned late that year and entered production in March 1966. Barwick became a full-time member of the writing staff and took over the role of script editor from the outgoing Pattillo. The main puppet cast and vehicles were rebuilt; in addition, the art department expanded some of the standing sets, including the Tracy Villa