From Halopedia, the Halo wiki
First Platoon was a Colonial Militia unit that fought at the First Battle of Harvest alongside Second Platoon. It was stationed near the cities of Utgard and Gladsheim, on Harvest. The leader of 1st Platoon was the then Staff Sergeant Avery Johnson. First Platoon consisted of 36 Colonial Militia recruits, divided in three squads of twelve recruits each.
On December 23, 2524, the Harvest militia began training for recruits, in order to handle internal security operations against the Insurrectionists, who were causing instability across UNSC-controlled space with terrorist attacks aimed at civilians. There were two platoons established; First Platoon and Second Platoon. Each platoon had been split into three squads, with twelve recruits in each.
The recruits of Second and First Platoon were trained for approximately three months when on February 9, 2525, they "graduated" from the Colonial Militia Training and were shown footage of the battle between their squad leaders against unknown aliens. Two days later, a pack of Jiralhanae from the Covenant arrived in a diplomatic meeting, in which the recruits provided security. However, a fight ensued, and Osmo, a member of First Platoon, was killed in the fighting.
On February 22, 2525, the platoons were stationed in Utgard while Staff Sergeants Johnson and Byrne and both platoons were sent to prevent the Covenant attack on Gladsheim, except for both Charlie Squads. However, they were too late and the town was destroyed and its population was slaughtered, except for one resident.
As the battle on Harvest progressed, the militia split to perform two operations. The first, led by Johnson, was a volunteer operation to secure the space-borne Tiara platform to ensure civilians evacuating in cargo freighters would safely leave the planet. The militia engaged Yanme'e, Unggoy, and Jiralhanae led by Tartarus. The Unggoy were killed with ease, but the other two alien species provided some difficulty. The operation was successful at the cost of seven militiamen's lives.
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