Complex sentence: They arrived in time to see service in the First World War and most survived to see make an extensive contribution to the Second World War effort, in the vital role of the convoy escort, freeing up more modern ships for fleet action.
Split into simpler sentences: They arrived in time to see service in the First World War. Most ships survived to make an extensive contribution to the Second World War effort, in the vital role of the convoy escort, freeing up more modern ships for fleet action.