The Planetary Defense Force (or PDF for short), is the primary defense almost all planets of the Imperium can muster in response to any threat. PDFs are raised from the local populace of the Imperial controlled worlds, who are also responsible for training and arming these men or women. They are raised on the authority of the Planetary Governor with the Imperium's authority and blessing.
In response to any threat, it is the responsibility of the PDF to engage the enemy until Imperial reinforcements can be mustered from the nearby sector. Thus although rarely respected due to their inherent lack of experience, PDF are widely considered crucial to the Departmento Munitorium, or else Imperial worlds would quickly fall to Xeno assaults or Chaotic influences.
Furthermore, PDFs are also the source of planetary tithes, the taxation the Imperium poses on all ruled worlds. The ability to call on the Imperium for military aid comes at a cost, and troops must be mustered and control given to the Imperium to assist other planets in need. Regiments founded for off world deployment are elevated into the Imperial Guard, and are bound for either greater honours and experience, or destruction.
Many PDF forces base their appearance and equipment off of the venerated Cadian regiments. Others base themselves off the appearance of other notable regiments, such as the Tallarn, Mordians and Valhallans, often motivated by similar climates or even due to assistance from those regiments during the founding of the PDF. Still, given the unique and underlying culture of many worlds, PDFs and by extension their Imperial Guard regiments are armed and appear as their world can best equip them, a sign of the diverse cultures that constitute the Imperium as a whole.
Although the PDF defaults all command to any Imperial forces that arrive, cultural conflicts, Xeno or Chaotic influences, the interests and corruption of the Planetary Governor or other organizations in charge of the planet, it is not uncommon for PDF forces to turn hostile upon off-world Imperial forces. This is a cause of mistrust for PDF in general, and further reason for commanders to prefer to rely on non-local defenses.
Inquisitors are particularly known for a lack of trust for the local PDF, often quick to have nearby Imperial forces available should need call for it.
Notable Planetary Defence Forces