The D.R.A.K. Rebellion was a conflict on Kamino where the Republic had asked Palpatine to end the cloning of the D.R.A.K. clones due to the fear of an inside rebellion because of their strength. Due to Palpatine putting the finishing touches on his plan to make the Republic into an Empire, his fears of the D.R.A.K. betraying him due to their closeness with the Jedi because of Drake had caused him to end the cloning. Ironically, this was what caused their rebellion against the Republic, not because they felt like it, but because of the mistrust.
During this rebellion, most of the D.R.A.K. clones returned to Kamino an took over a cloning facility, they used the computer to halt all of the cloning by hacking into the central system, crippling the Republic's Army from the inside. Multiple attacks had been launched, but the Republic could not break through. With the war with the CIS this rebellion that was ending the cloning process became too much and major attacks were initiated to end it.
The D.R.A.K.'s strength was too great as they used the narrow walkway's of Kamino as chokepoints, allowing them to beable to hold out for an extremely long time. With the D.R.A.K. winning an emergency plan was formed, an Orbital Strike was agreed on by the senate. Within moments the unexpectant clones found them selves being destroyed from space. The facility was destroyed and any D.R.A.K. clones who were able to survive the destruction died in medical facilitys.
Only a handful of D.R.A.K.'s were alive, those who didn't join the rebellion, they were not reticuled however as they came over betrayal. Drake and his "Brother" Omega254788 were some of them, Alpha 254 was thought to have died but later resurfaced and re-united the surviving D.R.A.K.s, they became an elite force who were not allied to anyone, they worked as high class mercenaries. Palpatine often hired them for certain missions after his formation of his Empire.
Shortly after the destruction of the D.R.A.K. Order 66 was given.