Complex sentence: Until that day, he was unofficially running the 2nd company of 502nd; however, he officially became the commander of 2nd company on the same day he was shot through the leg, arm, 4 bullets in the back and one through the neck.
Split into simpler sentences: Until that day, he was unofficially running the 2nd company of 502nd. He officially became the commander of 2nd company; on the same day he was shot through the leg and arm, received four bullets in the back and one through the neck.