Complex sentence: The Allies possessed little intelligence on western New Britain's terrain and the exact location of Japanese forces, so they flew extensive air photography sorties over the region, and small ground patrols were landed from PT boats.
Split into simpler sentences: The Allies possessed little intelligence on western New Britain's terrain and the exact location of Japanese forces. To rectify this, Allied aircraft many extensive air photography sorties over the region and small ground patrols were landed from PT boats.