And then there were (almost) five. Just a few weeks after Royal Caribbean ordered a sixth Oasis-class cruise ship, the cruise line has begun construction of the fifth sister ship – which is still unnamed.

Oasis 5 will be the largest cruise ship in the world when she enters service in 2021, and will be superseded by Oasis 6 when she is launched in 2023, following a Royal Caribbean trend of making each Oasis-class cruise ship incrementally bigger than the last.

Oasis of the Seas is the oldest of the world’s largest cruise ships, launched in 2009

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The newest Oasis-class ship Symphony of the Seas for example is the largest cruise ship in the world at 228,081 gross tons and carrying 6,680 passengers at maximum capacity, while Harmony of the Seas is 226,693 gross tons.

Similarly, Allure of the Seas and Oasis of the Seas are also smaller by a few thousand gross tons.

“We have gotten caught a little bit in our own loop, and so every time we introduce a new Oasis Class (ship), we always try to make it a little bit bigger so that it is the world’s biggest cruise ship,” said Royal Caribbean International President & CEO Michael Bayley when the fifth Oasis ship was first announced.

This fifth ship was ordered at the same time that Symphony of the Seas was delivered, and at the time Bayley confirmed that she would be even bigger than her four sister ships.

“It’s going to have to be a little bigger,” Bayley said. “Like an inch, three inches here; an extra few tons there.”

Executives from Royal Caribbean and Chantiers de L’Atlantique announce steel cutting for fifth Oasis-class ship

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Steel cutting for Oasis 5 was held Thursday at the French shipyard Chantiers de L’Atlantique. Executives from both companies presented the first plate of steel, which was cut during a small ceremony at the shipyard in Saint-Nazaire.

Steel cutting is the modern day equivalent to the keel laying, it marks the official start of a new ship’s construction. Oasis 5 will be built in sections like a Lego toy, with each massive block assembled and then welded together.

Royal Caribbean says this new, fifth Oasis-class ship “will combine the iconic seven-neighborhood concept that her sister ships feature with a bold and unexpected lineup of thrilling experiences, imaginative dining, unparalleled entertainment and the latest technology.”

She’s likely to feature the best of the existing Oasis-class lineup and the new Quantum Ultra-class, with Spectrum of the Seas recently delivered (and now on her way to Dubai) and her sister ship Odyssey of the Seas both boasting a range of new features and attractions.