- "Thunderdrum. This reclusive dragon inhabits sea caves and dark tide pools. When startled, the Thunderdrum will produce a concussive sound wave that can kill a man at close range. Extremely dangerous, kill on sight."
- ―Hiccup as he reads through the Dragon Manual.
the thunder drum
The Thunderdrum is a massive dragon that is as comfortable in and around water as it is on land. It is noted for possessing great power and a sonic blast for its breath attack, and is regarded as one of the most powerful dragons living. A Thunderdrum named Thornado was owned by Stoick the Vast, chief of the Hairy Hooligan tribe.
This dragon relies mostly on its two sets of wings, one primary and one smaller set to the rear, using them to get around and move through the water like a tornado. The Thunderdrum has legs (If you look closely in the book of dragons, you can see the legs.) Even though they are almost smaller and thinner than even a Terrible Terror's legs, they can surprisingly hold the dragons weight.
According to the Dragon Manual, a Thunderdrum is roughly the same size as an adult Viking, though they are clearly far larger (larger than Bucket and Mulch's ship as seen in How To Pick Your Dragon). All Thunderdrums seen in adaptations before How to Train Your Dragon 2 are not much larger than medium or large sized dragons, though their tails are very long.
In the How to Train Your Dragon 2 teaser, much larger Thunderdrums are seen. These Thunderdrums are about as big as baleen whales and their wingspan is long enough for Toothless to fly under one that was jumping out of the water. This dragon is reclusive in nature, living in sea caves and dark tide pools or even in open waters. The Thunderdrum is classified into the Tidal Class, along with the Scauldron, Bewilderbeast and Seashocker. The maximum size for these dragons is unknown.
They form pods in hunt or on migration, and take care of each other and can be compassionate, and these features are similar to those of cetaceans. The Scauldrons also share at least the first of these traits (most of seen specimens had not been calm at times), and both of them are whale-like dragon kinds.
The name comes from its main mode of attack/defense. Instead of breathing fire, the Thunderdrum produces a strong concussive sound that can kill a human at close range. Not only temporally stunning other dragons, but also these waves of sound and air can even extinguish flames shot by other dragons. The blast is so powerful that the creature is said to "get its power from Thor himself." Only the Screaming Death has a tolerance with this attack (capable to stun it temporally). Like nearly all dragons in the Manual, they are classified "extremely dangerous, kill on sight." It is also said that when a Thunderdrum hatches from its egg, it makes a sound so loud it rattles the sky.
Understandably, they are strident and assertive, the loud Thunderdrum always makes its feelings known! 
The Thunderdrums can shoot blue blasts that get bigger the farther they go. Those fire blasts also travel at the speed of the sound.
They are also considered to be one of the most omnipotent and useful of all dragons in terms of orbit. These marine dragons are capable of flattening their bodies by expelling oxygen from lungs for a limited period of time, and enhance underwater mobility from to skim on water surfaces to dive deeper for feeding.
These dragons have stubby legs and long, skinny tails. When they open their enormous mouths, they show a series of teeth inside. Their wings are large triangles. It has a horn on the tip of its nose. It also has a series of backwards facing spikes sticking out of its back. The Thunderdrum, because of all that, is closely related to the Whispering Death , except the Thunderdrum has limbs, bigger, triangular wings, it's eyes are lifeful, the Thunder Drum's torso expands with it's mouth, and the Thunder Drum has the ability to close its mouth. The Thunderdrum's body resembles several marine megafaunas such as a basking shark, a whale shark, a manta ray, or a baleen whale. Its head somewhat resembles that of an angler fish. Several other dragons share similar head shapes such as the Skrill and the Flightmare. In Riders of Berk this dragon is just bigger than Stoick (excluding the tail), but in the How to Train Your Dragon 2 preview, it is much bigger.(if you look at these Thunderdrums from the side just the mouths are the same lenght as Toothless' entire body, including his tail.)
The Thunderdrum appears in this exclusive short. It is classified into the Tidal Class in the book. Bork the Bold once found the egg of a Thunderdrum. But he didn't know that Thunderdrum eggs hatch with an explosive sound that rattles the sky, and he found this out the hard way.
In How to Pick Your Dragon the Thunderdrum was first labeled as a rogue dragon attacking Berk's fishermen out at sea. While Hiccup tries to find Stoick a dragon so he can help his village more effectively, the rogue dragon strikes again. When they arrive on scene, Stoick is satisfied with the beast and requests his son to train it. However, when they bring it back to the academy and put a muzzle on it to keep it from using its roar on This dragon is picked for its ferociousness by Stoick the dragon becomes too stubborn and eventually breaks free.
After finding it, Stoick and Hiccup learn that it was accompanied by another Thunderdrum that was injured, which is why it attacked the fishermen, so it could get food for its friend. Hiccup leaves to fetch the others while Stoick stays behind with the Thunderdrums, but they are soon ambushed by wild boars. Stoick finally bonds with the dragon and together they defeat the boars.
n Dragon Flower, Stoick reveals to have named his Thunderdrum Thornado. His dragon is shown flying his master to the Shivering Shores as there was a meeting with their chief. When Stoick returns, Thornado eventually becomes ill from the Blue Oleander that Mildew planted. By the end of the episode, Thornado is cured with a Scauldron's anti-venom.
In What Flies Beneath, Thornado returns again. He is ridden briefly by Stoick into battle with the Whispering Death. He uses his sonic roar on the enemy dragon, but it has little effect. Before Thornado and the other dragons can close in, Toothless calls them off.
A herd of gigantic Thunderdrums were seen in the Teaser trailer, as well as in the new trailer, and the first five minutes.
Dragons: Wild SkiesEdit
In Dreamworks Dragons: Wild Skies, the Thunderdrum can be tamed. It lives in Wrecker's Reef, and one must feed it crabs or fish in order to tame it. You will need 10 Gold and buy a Crab Net, then go to Wrecker's Reef, where you then select the crabs. The Thunderdrum is a Tidal Class Dragon, and it screeches instead of breathing fire. When the player rides it, the dragon's mouth is closed. When you press the space bar, it will open its mouth and screech at the target. Other Vikings will say that the player is as strong as Stoick after having tamed it.
The Thunderdrum is also seen in School of Dragons. Only members can own a Thunderdrum. Stoick's Thunderdrum Thornado appears in the quest 'The Sickly Dragon' wherein Thornado is seen sick and you have to find mint leaves in the wilderness which is made into tea.