Clash of Clans: Dark Barracks

Dark Barracks allow you to train Dark Elixir Troops using Dark Elixir. These troops will be stationed in Army Camps. Dark Barracks are unable to function while being upgraded, considerably increasing the time it takes to train your armies; this should be taken into consideration when deciding to upgrade a Dark Barracks. Any Troops that are queued up inside will start training when the upgrade has been finished.
Once you have queued Troops in your Dark Barracks, you can instantly complete their training with Gems; the amount required is directly proportional to the amount of time remaining to finish training normally.

There is also an option to boost Troop production for 2 hours. The boost option costs 10 Gems and will increase the training speed of the boosted Dark Barracks by a factor of 4.
The boost timer will continue to count down even if you aren't making troops, so don't boost your Dark Barracks until you are ready to use it. When you click to boost the Dark Barracks a clock appears for a few seconds. Similar to the normal Barracks, Troops may be removed from the Dark Barracks training queue at no penalty; 100% of the Dark Elixir cost will be refunded to you.

You may queue more Troops than your Army Camps can hold. This is useful for two reasons:
You may queue Troops prior to engaging in combat (either single-player or multiplayer). Your Dark Barracks will begin creating Troops proportional to the amount of time you spent from when you start searching for opponent to completing an attack, significantly reducing your downtime between battles

You may queue Troops to 'hide' Dark Elixir while you are offline, as long as your Army Camps are full. Currently up to at least 5,030 Dark Elixir can be hidden in this fashion (seven level 2 Witches and one level 5 Hog Rider in each of the two level 6 Dark Barracks). When you return you simply un-queue all of your Dark Barracks to reclaim your hidden Dark Elixir.

A Dark Barracks will maintain its queue if destroyed by enemy Troops, and will even continue to produce new units if your Army Camps have sufficient space.
The Dark Barracks is the only Barracks in which you are allowed to create Dark Elixir Troops.