Complex sentence: It had been proposed that US First Army be inactivated, but its commander Lt. General Robert W. Porter, Jr. strongly protested the proposal and it was dropped, but the old Second Army headquarters staff were retained and became the new staff for U.S. First Army.
Split into simpler sentences: It had been proposed that First Army be inactivated, but its commander Lt. General Robert W. Porter, Jr. strongly protested the proposal and it was dropped. In the end, Second Army headquarters staff were retained and became the new staff for U.S. First Army.