Supercell announced the following in their June 2018 update:
The release of Town Hall 12 brings a weaponized Town Hall, new building levels, balance changes, and more content yet to be revealed. However, one of the most exciting features being introduced to Clash of Clans is the SIEGE MACHINES!
What are Siege Machines?
Siege Machines introduce a wholly new gameplay mechanic to your Village. Smash through Walls! Bomb defenses! Deliver your Clan Castle reinforcements directly into the heart of your enemy’s base!
These mobile Clan Castles are trained in the Siege Workshop, a new building available to Town Hall 12 players and will carry and protect your Clan Castle reinforcements into combat.
What Siege Machines do?
Siege Machines will attempt to drive straight for the enemy Town Hall in order to disgorge its complement of troops. Each type of Siege Machine will offer a unique method of transporting and deploying your reinforcements during your attacks, but more details on this later. Once the Machine has reached the Town Hall it will self-destruct, releasing the Clan Castle troops within.
Will only Town Hall 12 be able to use Siege Machines?
No! While the Siege Workshop can only be built by Town Hall 12 villages, Siege Machines can be donated to your Clan mates of Clan Castle level 6 or higher! Use them as a new and effective strategy during Clan Wars!
What kind of Siege Machines are there?
With the release of Town Hall 12, there will be 2 Siege Machines available: the Wall Wrecker and the Battle Blimp. Both reach their objectives in their own way and open new avenues of how you will not only build troop compositions but also how you can defend against them.
The Wall Wrecker
The Wall Wrecker has two purposes in life: To smash through anything that stands in its way and provide an armored shell of heavy-duty materials to protects its precious cargo. The Wall Wrecker will plow through Wall pieces (doing damage x10) and will hammer away at any other building along its path. Not only does the Wall Wrecker provide a way to shield your Clan Castle troops from oncoming assaults, it opens up new strategies for funneling your army as the Wrecker clears the way to victory!
The zippier, hot-air filled cousin of the Wall Wrecker, the Battle Blimp soars over your enemy’s defenses. As it beelines directly for the enemy Town Hall, the Battle Blimp will drop a continuous barrage of bombs. The Battle Blimp is much faster than the Wall Wrecker but will take less damage before it ultimately is forced to drop its payload. Just fill the Battle Blimp with Valkyries, drop a Rage Spell on the enemy Town Hall and watch the chaos ensue as the Valkyries create a whirlwind of destruction when they’re dropped from the skies.
How do I use a Siege Machine?
If you have trained or received a donated Siege Machine, they will show up on your available Troops list and are deployed the same way you deploy your other units. When you receive Clan Castle reinforcements from your Clan mates, you will be presented with a new button on the user interface (UI). You can choose to deploy your Clan Castle troops normally by pressing the Clan Badge icon and attack the old-fashioned way…or…you can choose to SMASH your way to the Town Hall with a SIEGE MACHINE!
When you deploy your Siege Machine, your Clan Castle troops are automatically placed inside and will remain inside until one of 3 things happens; 1) they reach the enemy Town Hall 2) the Siege Machine is destroyed or 3) you can self-destruct the Siege Machine to manually deploy your troops.
No matter which way you use them, your Clan Castle troops will be released and will be allowed to cause havoc.