From Halopedia, the Halo wiki
Around the time Master Chief John-117 arrived on the fragmented section of Zeta Halo, Thunder Squad's marines were holed up inside a cave when they were attacked by Banished troops. At some point after the Chief stormed the Tower and killed Chak 'Lok, the Spartan's AI companion, The Weapon, picked up Thunder's distress call, prompting the Chief to rescue the marines.
In Halo Infinite, Thunder Squad is found in the "Connections" section of the campaign. Answering their distress call earns the player 30 Valor points. This valor is awarded even if all members of Thunder Squad are killed.
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