In fact, his original posting to the Pillar of Autumn put him in command of ~32 Spartan IIs for a long range mission into Covenant territory to capture a Covenant ship and possibly one of the ruling class (now known as the Prophets). Things got SNAFU when the Covenant attacked planet Reach. He sent a majority of the remaining Spartans on-planet to defend the fusion reactors powering the super orbital MACs while he went on a side mission with two other Spartans (Linda and Joshua IIRC...) to ensure the destruction of an ONI Section III ship that was docked in one of the orbiting space stations.
Joshua got sent off into space - MIA - and Linda was severely wounded and put into cryo-stasis aboard the Pillar of Autumn. Reach was lost and presumed glassed just as the Pillar of Autumn made a pseudo-random jump into hyperspace to escape; Cortana secretly used stellar coordinates found previously on some Forerunner artifact.
In Halo: Combat Evolved, you can actually go past that section in the first level where you see through the glass windows and the Elites are there "searching for you". There's a screen on the work station there that shows a schematic of your Mjolnir suit. If you go into the room behind you, you'll find a somewhat identical room with another screen showing the same schematic for a Mjolnir V suit, but the blast shields have been lowered - Linda!?