Complex sentence: But Young's hearing and eyesight had gotten worse and, shortly before the 148th landed on New Georgia, concerned that this might affect his ability to command his squad in combat and put them at risk, Young requested that his rank be reduced to private.
Split into simpler sentences: But Young's hearing and eyesight had gotten worse, and he became concerned that these deficits might affect his ability to command in combat, putting his squad at risk. To eliminate this risk, shortly before the 148th landed on New Georgia, Young requested that his rank be reduced to private.