Welcome to our Thunderbirds Deep Dives! As we celebrate International Rescue's 60th anniversary, we asked you to pick your favourite episodes of Gerry and Sylvia Anderson's classic 1965 sci-fi adventure series that should receive in-depth, analytical retrospectives. Based on your picks, we've collated a top 10 selection of Thunderbirds greatest episodes to receive a review - as voted for by you!

We're continuing our Thunderbirds Deep Dives with a beloved episode that's entirely appropriate for the forthcoming spooky season - Attack of the Alligators! In this deadly mission for International Rescue, Thunderbirds turns its attentions away from out-of-control vehicles or collapsing super structures and focuses on something far more primal in its menace.

Tonal trajectories

Throughout our Stingray Deep Dives last year, we explored how the series evolved its tonal trajectory during its run - specifically, how it embraced more offbeat storylines and grew an increasingly strong sense of tongue-in-cheek humour with its storylines. We notably shifted from the core underwater Cold War premise to pop idols, jazz bands and movie stars. Thunderbirds pursues a similar evolutionary path. Towards the end of the first series' run, storylines shifted away from the usual techno-disaster fare to become rather more unpredictable and humorous in their scope.

By the end of Thunderbirds' first series, International Rescue's danger zones involve exploding dog food (Danger at Ocean Deep), aristocratic heists (The Duchess Assignment), mutant reptiles (Attack of the Alligators!) and military aircraft terrorism enabled by pop music (The Cham Cham). Attack of the Alligators! reads like script editor Alan Pattillo casting his editorial eye over what Thunderbirds had achieved at that stage, and determined what else the series could achieve.

From children's TV to horror cinema

Attack of the Alligators! marks Thunderbirds closest dalliance in shifting from a children's TV series and into becoming a horror movie. Given all the other genre territories that Thunderbirds dalliances with across the series (action, comedy, romance, drama), why shouldn't the series embrace horror? The infamous alligators who deliver the episode's raucous, violent drama are the key signifiers of horror here (very real junior reptiles were used during production), but the episode's whole package is a step outside of Thunderbirds' comfortable tonal retrofuture territory. Through spectacular attention to detail in the episode's production values, with its isolated, swampy setting, and compellingly uncomfortable characters in the form of boatman Kulp and housekeeper Mrs. Files, the episode succeeds in its sense of heart-stopping unease.

Scriptwriter Alan Pattillo casts fresh emphasis on how Thunderbirds' predicts future developments of society. Businessman Blackmer's visit to Doctor Orchard's isolated laboratory is to witness Orchard and his assistant's astounding discovery of thermaine, a liquid substance found only in these murky backwaters. Theramine is to be the cure for 2065's escalating food shortage supplies, a subtle reflection of population growth and its subsequent demands on the world around us. 

Director David Lane and special effects maestro Derek Meddings effortlessly craft a smothering sense of foreboding with the setting of the grand yet dilapidated house from which Orchard is carrying out his experiments. Cramped camera angles signify the densely packed quality of the swamp, lingering wide shots of the landscape capture its sprawling qualities. All the while guarded by alligators, which, for now, appear harmless enough...

Boatman Kulp is one of Thunderbirds' black-hearted villains. Brought to life with a fantastically evil performance from David Graham, the thuggish Kulp is driven by pure greed to steal theramine for himself and the supposed riches it may bring. There's no masterplan at work here - Kulp is purely opportunist and cowardly, and his theft goes horridly wrong when the theramine is accidentally spilt into the water supply, infecting the alligators, causing them to enlarge and become unstoppable creatures of destruction. 

It's unfortunately tricky to discuss Attack of the Alligators! without acknowledging the cruel levels which the special effects crew went to in ensuring the creatures acted the way they desired. The episode utilised genuine alligators, which were sadly subjected to electric shocks to stimulate and antagonise them. While their enthusiastic performances remain hugely memorable, these behind-the-scenes details undeniably lend a bitter aftertaste to the episode's thrilling jeopardy. Tellingly, the alligators rarely interact with the puppets, instead confined to the special effects stages. The seamless blend of puppet and alligator scenes are brilliant to watch unfold, the alligators' increasing violence made to feel within reach of the entrapped characters when the monsters attack the nearby house.

Death-defying rescues

International Rescue's presence in Attack of the Alligators! is a curious mixture of death-defying rescues and oddly inconsequential filler scenes. The Tracy family's scenes in the episode mostly amount to the rescue operation itself, but they open with the scenes of Alan being dispatched to fix Tracy Island's damaged radio communications. They're unusual scenes in that they have no wider contextual place in the episode, and IR's communications blackout doesn't come into play at all during the rest of the episode. The scenes otherwise break up the pacing and allow us to visit Tracy Island before the rescue takes place, but otherwise, it comes off filler material needed to bulk out the episode. If so, it's striking that, at this late stage in Thunderbirds' production, episodes were still struggling to find suitably engaging material to meet their 50-minute runtime. 

The rescue operation makes use of all five Tracy brothers, reflecting the level of danger provoked by the creatures, but the episode really escalates the jeopardy by emphasising the dramatic potential of Thunderbird 1's function to arrive at the danger zone quicker than Thunderbird 2. Scott's efforts to defend the occupants of the house from the marauding alligators is complicated by Kulp's hostile takeover of the situation, injecting a further level of spiralling chaos into the already grim situation. 

Virgil, Gordon and Alan's efforts to tranquilize the alligators is swiftly executed, even if our minds rear back to just how these alligators were made to move in the first place - or not move. This episode also prizes open a head-scratching aspect of Thunderbird 2's operational set-up. Despite Jeff Tracy's instruction to carry Pod 6 to the danger zone, it's revealed to contain Thunderbird 4, which supposedly exclusively lives in Pod 4. Evidently then, pods can be adapted to suit varying disaster scenarios - which rather contorts the logic of bothering to have six 'different' pods? 

Alan's characteristic impetuousness in tangling with the last alligator standing injects a sudden surge of personable drama into an already carnage-fuelled rescue mission. It's enjoyably remarkable how Attack of the Alligators! still finds room to further intensify the situation by thrusting Scott and Alan into their respective dangerous spots. But the threat of the alligators can't be successfully calmed before the despicable Kulp gets what he deserves.

It's amusingly bleak that Kulp's sudden death when trying to escape only provokes International Rescue into further action due to the loss of Kulp's phial of theramine, rather than rescuing Kulp himself. That quiet acknowledgement that this wasn't a character worth saving may be him getting his just desserts, but it rings oddly hollow that Kulp's horrific death goes uncommented by International Rescue.

Fantastically enlarged and unstoppably violent creatures were the kind of danger zone territory generally reserved for Thunderbirds' spin-off media, likely because outlandish creatures were easier to conjure up in comic or novel form than on the small screen. Attack of the Alligators! is a firm reminder of the wild ambitions AP Films harboured in pursuing the most daring forms of adventure for their puppet creations. Both the runaway nature of the enlarged alligators during the episode's events and the very real pain the creatures were subjected to behind-the-scenes serve as cautionary reminders of the darker undercurrents than run beneath such ambitions.

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