From Halopedia, the Halo wiki
First introduced to UNSC service in the latter years of the Domus Diaspora, it would see use with the UNSC Army until the early years of Operation: TREBUCHET. During this service, the Viper's design led it be used to direct fire support and acting as a mobile response. The larger Scorpion would take on other frontline roles.
The M700 Viper was originally planned to be added to Halo: Combat Evolved, and known only as the "Stealth Tank". However it ended up cut from the game. As part of the Digsite Alpha initiative for Halo: The Master Chief Collection, the vehicle will be added back into the game as the "Viper". The choice of the "Viper" name was the result of an informal competition among the Digsite team.
The stealth tank was originally built and designed by Marcus Lehto. He designed it as a lower, stealthier vehicle to complement the M808B Scorpion, featuring a "low profile with counter vented fire stabilization".