In an effort to optimise each Spartan's field competencies and test skunkwork modifications, the Project: COBALT suits' titanium alloy frame were temporarily modified from their baseline Mark IV iterations to bear distinctive features. The COBALT suits had prototype stealth technology that was in each suit, with the plating being tinted with the same refractive coating employed on the Office of Naval Intelligence's Prowlers.
- COBALT CV.117: CV.117 featured prototype stealth technology and a customized surveillance drone. Worn by John-117 during the Battle of Alpha Corvi II in 2525, and in Operation: SILENT STORM and the later Battle of Netherop in March and June 2526.
John-117 wearing the CV.117 on Biko.
- COBALT MV.104: MV.104 featured carbon-fiber blades housed in the forearms of the armor. The blades could be locked in place or could be fired as a projectile for up to a hundred meters away, with them also having embedded beacons linked to internal displays for potential battlefield retrieval or vehicle tracking. Worn by Fred-104 during the Battle of Alpha Corvi II.
- COBALT SV.058: SV-058 featured advanced optics and rangefinder technology to enhance visual acuity on targets across a range of spectrums and environmental conditions. Linda-058 requisitioned a twin-engine external VTOL propulsion device that could be deployed to allow for rapid relocation at a moment's notice.  Worn by Linda-058 during the Battle of Alpha Corvi II.
- COBALT RV.087: RV.087 was outfitted with additional accoutrements that aided in reconassence and high-speed terrain traversal. The suit also had sensor suite designed specifically for accurate and timely battlefield analysis during extra-vehicular activity scenarios. Worn by Kelly-087 during the Battle of Alpha Corvi II.