One year after the Time War began, Compassion agreed to help the War King of Gallifrey with the 103-Form breeding project. The male parts of project were provided in the form of specially constructed bull-TARDIS Engines. After mating with one of these, Compassion produced her first born son - Antipathy. Antipathy was probably classified as a 103X Form. Antipathy was experimental, incomplete and unformed. The Time Lords sent him on a "test mission" that was, in fact, a suicide mission, but he consumed his operators and managed to escape. Time Lords began breeding several Type 103A War TARDISes to fight in the Time War. These TARDISes were produced through "organic" mating instead of being constructed in Solar Workshops. Many of these TARDISes are produced on Simia KK98. All Type 103s are female. Almost all Type 103 Operators are male. The male/female breeding system ensures that each 103-Form has a mutagenic factor to make them less vulnerable to manipulation at the hands of the Time Lord's enemies. These TARDISs are bred to be aggressive and sentient.

These 103-Form TARDISes are the most essential and useful weapon the Time Lords have in the War and they quickly became the most common TARDIS in the War era. The Time Lord operator's primary purpose in a 103-Form is maintenance. A whole new culture and vocabulary is created to deal with Time Lord/TARDIS interaction. A 103-Form provides an operator with protection and a physical home, and an operator provides a 103-Form with a social/political foundation. While the 103-Forms have most the abilities and features of Compassion some of their capabilities were probably deliberately capped, making them less powerful then their 102-Form mother.