Complex sentence: The first vessel is due to enter service with the Royal Navy sometime during 2021 and by the mid- 2030s the Type 26 will be the backbone and workhorses of the Royal Navy.
Split into simpler sentences: The first vessel is due to enter service with the Royal Navy by at least 2021. By the mid- 2030s the Type 26 will be the backbone and workhorses of the Royal Navy.