Complex sentence: Meanwhile, three Beaufighters of No.30 Squadron RAAF had arrived at Milne Bay on 5 September, an additional six Beauforts of No.100 Squadron RAAF joined them the following day, tasked to provide additional support against any further landings and undertake anti-shipping missions.
Split into simpler sentences: Meanwhile, three Beaufighters of No.30 Squadron RAAF had arrived at Milne Bay on 5 September. An additional six Beauforts of No.100 Squadron RAAF joined them the following day, tasked to provide additional support against any further landings and undertake anti-shipping missions.