In the Battlestar Leonidas's Universe, the Viper Mark IX "Pilum" is the first Viper design not to replace an older Viper. While the Admiralty was happy with the Viper Mark VIII, it was costly to build because of it hyperdrive. So the Colonial Governemnt orders a new supplemental Viper be design. It was design to be the next generation space superiority fighter. The Viper Mark IX could reach great speed than the Viper Mark VIII. At the time of the Cylon attack it was still in the design stagle. While it mounting twin 30mm autorailgun on the wings, and two 40mm cannon in the hull. However it lacks the hyperlight drive of the Marathon and Sidewinder in order to have room for the larger cannons & ammunition. It also lost the the ability to carry and launch missile so it could have a greater speed. It was mention in Chapter 2 of Volume 4, that is was three month from having the protoype ready.
Images and most of the information is taking from deviantart and was created by Barricade.