From Halopedia, the Halo wiki
The 957-A3 was a locally-produced variant of the M808B Scorpion tank in service with the UNSC during the Human-Covenant War. It was codified by the UNSC Army. The tank featured enhanced electronics for more accurate firing. As well as it modifications, it had what appeared to be an arrowhead or lambda symbol painted on its left front tread cover.
In 2552, a 957-A3 was assigned to the UNSC In Amber Clad. In October of that year, during the Battle for Earth, the tank was deployed in the industrial zone of New Mombasa to defend a Lethbridge Industrial building housing A Company from Covenant forces. Shortly after John-117 arrived, a Scarab walker started to advance on their position. The 957-A3 used its main cannon to fire on the walker, but to no avail. Within seconds, the Scarab's focus cannon destroyed the tank, killing the vehicle's operator.
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