Command Destroyer
Command Destroyers (sometimes abbreviated CMDD) are T2 destroyers which are designed for fleet support. They can fit one Command Burst module but often fit a Command Processor rig to fit a second Command Burst. Further, they have a 2% bonus to their factions Command Bursts for each level of 
Command Destroyers and a 95% reduction in powergrid requirements for Command Bursts. This makes them the only viable hulls to use command bursts below crusier sized ships.
Their other defining feature is the ability to fit a Micro Jump Field Generator (short MJFG, also called boosh). This module jumps the Command Destroyer and every ship in a 6km radius 100 km in the direction the Command Destroyer faces as long as they are not scrammed or invulnerable (for example due to gate cloak or tether). MJFGs have a base activiation time of 9 seconds. The jump only happens after this spool up time. This spool up time is reduced by 5% for each level of Command Destroyers and Micro Jump Drive Operation.
On top of the already mentioned bonuses, they all have a 50% reduction in Microwarpdrive signature radius penalty. The empire faction's Command Destroyers also have a 4% bonus to resists for their faction's tank per level of the T1 destroyer skill. This results in a 20% resist bonus. They also have a 10% damage bonus per level. The Triglavian command destroyer doesn't follow this pattern but has a 10% range and a 20% damage bonus but no resist bonus.
The different Command Destroyer hulls are:
Tactics
The ability to use Command Bursts makes Command Destroyers typical force multipliers because they improve the performance of all ships in the fleet. While Command Bursts are straight foward in their tactical use, the Micro Jump Field Generators lead to more creative tactics. This ranges from booshing ships off from gates or stations to prevent them from jumping or docking, over splitting hostile fleets (expecially logi) to make it easier to kill them, to full booshing doctrines in which a big number of Command destroyers allows to use booshes in short succession to rapidly move around. It is worth to note that while Command Destroyers are usually fleet ships they can also used as solo ships.
Fitting
Command Destroyers always fit a Micro Jump Field Generator. Besides that they can be afterburner or microwarp drive fitted, sometimes even both. They often fit a warp srambler. So that they can decide when to drop scram because scram prevents ships from being booshed. All other fleet members should only use points on targets in such a context. ECM bursts are another common module. It allows to break hostile target locks in case the Command Destroyer or fleet members are scramed which would prevent the fleet from booshing out.
The slot layout and bonuses usually force an armor tank for the Pontifex and Magus and a shield tank for the Stork and Bifrost. In a fleet context you fit a buffer tank, while solo fits can have an active tank.
If the Command Destroyers primary role is to provide Command Burst, a Command Processor rig is usually fitted to allow two active Command Bursts. In a booshing doctrine some might not even fit a Command Burst at all.
A defender missile launcher is a popular choice to protect the fleet from bombs.
History
Command Destroyers were introduced in the Frostline expansion (Dec 2015).
