Complex sentence: The Pola Flotilla had a maximum strength of 33 U--boats; due to the favourable conditions for commerce raiding in the Mediterranean, they caused a disproportionately large number of Allied losses during the U-boat campaign.
Split into simpler sentences: The Pola Flotilla had a maximum strength of 33 U--boats. Due to the favourable conditions for commerce raiding in the Mediterranean, they caused a disproportionately large number of Allied losses during the U-boat campaign.