Numbering only at twelve, the Null-class Advanced Recon Commandos, also known as Null-ARC's, were the first clones of Jango Fett created by the Kaminoan cloner: Orun Wa, and the prototypes for the Republic Army as well as the first batch of ARC-Troopers. They were deemed a failure by the Kaminoans and were not put into mass-production.
Most Nulls were named after Mandalorian warriors.
Although it was believed that only six had survived the gestation process, it is later revealed that the other six Null ARC's did indeed survive, through the efforts of a Kaminoan named: Nala Sena, who desired to study the Null-ARC's case furthurmore. Eventually, a second batch of Null-ARC clones were created by Nala Sena.