Initially built as a multi-role strike craft the ISB-21 is a modular design with the base model designed as a stealth bomber due to the craft's heavy armor, stealth coating, and a miniaturized FTL Engines. This however quickly changed many within the Imperial Military realized that the Revenant can easily be transformed into a troop transport, close-air support aircraft, Electronic-Warfare craft, and even an emergency boat should the need arise.
Therefore the proud designers at Akita Technologies went to work quickly converting the craft into various modular designs with the ISB-21 standing for Strike Bomber while the ITT-21 stands for Imperial Troop Transport and the AC-21 standing for Attack Craft.
The design itself is rather simple with each component of the craft easily interchangeable with other "Kits" resulting in a troop transport with the engines of a Long Range Bomber or vice versa. However this does not mean the Revenant is perfect as the designers of the craft did not expect to upgrade their initial design for another decade due to the near perfect frame.