Complex sentence: With D Company facing at least a battalion 12 Platoon attempted to move up on the right at 17:15, fighting off an attack on their right as they advanced, before pushing forward another.
Split into simpler sentences: With D Company facing at least a battalion 12 Platoon then tried to move up on the right. Stepping off at 17:15, they fought off an attack on their right, before pushing forward another.