Complex sentence: In 1999, a new ship LÉ "Róisin" was delivered to the Navy, marking the beginning of a new class of larger patrol vessels followed by LÉ "Niamh", commissioned in September 2001.
Split into simpler sentences: In 1999, a new ship LÉ "Róisin" was delivered to the Navy, marking the beginning of a new class of larger patrol vessels. The most recent addition to the fleet has been LÉ "Niamh", commissioned in September 2001.