A PDC (Point Defense Cannon) is a rapid-fire projectile weapon used by all military-grade spaceships for defense against small ships and missiles.
PDCs are Gatling cannon turrets, utilizing a set of spinning barrels to spew out thousands of rounds per minute to intercept incoming ordinance. They come in sets to cover all angles with overlapping fields of fire, providing a "curtain of steel" to more easily and effectively take out missiles.
PDCs are likely computer-controlled, as even juiced-up human gunners would find it nearly impossible to effectively track and destroy supersonic targets like torpedoes. The cannon turrets can also be retracted into the hull.
PDCs are largely for use against ordinance, but they also perform fairly well as CQB ship-to-ship weapons and can be used for direct air-to-surface strikes on personnel. The rounds seem able to pierce most ship hulls.
PDCs first come into use on the MCRN Donnager, which uses her numerous PDCs to shoot down a hail of plasma torpedoes launched by an attacking squadron of Stealth Ships. While most of the torpedoes were shot down, the advanced guidance systems of the torpedoes, as well as their numbers, allowed one to get through and damage the Donnager's reactor. In the ensuing CQB battle, Donnager used focused fire from her PDCs to destroy at least one assailant. As the Tachi (later to be named Rocinante) escaped the Donnager's hanger bay, under a hail of small arms fire, it returned fire with its PDCs to wipe out many boarders and blow open the hangar door, allowing the ship to escape.
At the Battle of Thoth Station, Rocinante's PDCs were used to intercept torpedoes, destroy an anti-asteroid cannon on the station, and even take out the far better equipped Stealth ship by riddling it with thousands of holes at point blank. The enemy also used their PDCs to disable one of Roci's port-side thrusters, hampering her maneuverability during the battle until Amos repaired the damage.
During the Ganymede Incident, PDCs were used as the main weapon between MCRN and UN ships engaging in combat in Ganymede's orbit, destroying ships on both sides as well as several orbital structures, resulting in a cloud of debris falling to Ganymede's surface and the loss of thousands of military personnel.
- PDC rounds are repeatedly described as "Teflon coated Tungsten". While not explained in detail in the books this fact could make PDC rounds "armor piercing sub-calibre ammunition;" a long narrow Tungsten arrow acting as an armor breaking component, surrounded with light Teflon-edged sabot, providing maximum barrel exit velocity.
- The Teflon does not affect the ballistics of the round used, but rather allows for harder armor-piercing materials like tungsten to be used without excess barrel wear, as the Teflon lubricates the bullet, allowing it to better engage the barrel without grinding it down. This would be a valuable trait in Gatling ammunition, as with the very high rate of fire, harder AP ammunition would wear down the barrels quickly.
- In the book, unguided weapons, like the PDC and Railgun, are described as being viable only with ranges of less than 1000km. Given that PDC rounds are far slower than Railgun slugs, thus more easily their effective range is presumably much shorter than even that. Based on the length of ships like the Donnager compared to the visual range at which PDCs are used, this effective range seems to be between 1-5 km.