Originally Published: 20 JUN 21 15:30 ET

Updated: 21 JUN 21 12:49 ET

By Marnie Hunter, Leyla Santiago and Sara Weisfeldt, CNN

(CNN) -- A trial cruise set sail from Miami on Sunday evening, putting the cruise industry one step closer to resuming operations out of US ports, 15 months after the Covid-19 pandemic brought cruises to a halt in the United States.

Royal Caribbean's Freedom of the Seas departed from PortMiami around 7 p.m. with about 600 employee volunteers on board to test Covid-19 health and safety measures before the ship starts welcoming paying passengers.

All of the volunteers are vaccinated, Royal Caribbean said, and there is a representative from the US Centers for Disease Control and Prevention on board.

According to requirements outlined by the CDC, a trial cruise is one of two paths for a cruise ship to resume sailing.

A ship may either opt to perform a trial cruise or agree to set sail with almost all fully vaccinated passengers and crew -- 95% for both groups.

Patrik Dahlgren, senior vice president of global marine operations for Royal Caribbean Group, told CNN it's been a long and evolving journey for the company to get to the point where it is ready to safely cruise again.

"We engaged the greatest experts in this country and in the world in terms of setting out what measures should we have in place," he said.

"How do we avoid and prevent cases from coming on board to the max extent and how do we mitigate them onboard the ship, leveraging technology, leveraging testing? And of course the big game changer is really the vaccines, and that has really changed everything for us," he said.

However, Royal Caribbean has bucked the trend of requiring the majority of its passengers on upcoming sailings from Florida to be vaccinated.

Vaccines are strongly recommended for Florida sailings and "unvaccinated guests must undergo additional COVID-19 testing at their own expense," according to the cruise line's website on June 20.

"We do strongly recommend all the guests be vaccinated for sure for those who are eligible, but we have measures in place to keep the cruises safe," Dahlgren said. The measures include some areas with social distancing and more medical capabilities on the ship.

Getting back to sea

The path to resuming operations has been complicated.

In April, Florida challenged the CDC's authority over cruise industry practices in a lawsuit, and Friday, a federal judge ruled the CDC's conditional sailing order on the cruise industry "likely constitutes an unconstitutional delegation of legislative power to CDC."

Florida Gov. Ron DeSantis filed the lawsuit against the CDC and called the decision a "major victory."

Dahlgren said Royal Caribbean is still looking at the possible impact of that ruling on its operations, future test cruises and adherence to the CDC's conditional sailing order.

The vaccination question has also been a contentious one, as Florida is one of several states that has banned businesses from requiring customers to provide proof of vaccination.

While Royal Caribbean is not requiring passengers to be vaccinated in Florida, guests sailing on upcoming cruises to Alaska out of Seattle will have a vaccination requirement.

Meanwhile, several other cruise lines have already announced plans to sail from Florida this summer with vaccination requirements in line with the CDC's 95% criterion.

The first voyage with paying passengers is set to embark from Fort Lauderdale on June 26 on Celebrity Cruises' Celebrity Edge ship with 95% of passengers and crew vaccinated.

But first is Sunday's inaugural trial voyage aboard Freedom of the Seas. It will last two nights with a stop at Royal Caribbean's private island in the Bahamas, Perfect Day at CocoCay.

Klaus Meisel, one of Royal Caribbean's employee volunteers on the trial cruise, is feeling good about the voyage.

"We'll follow the protocols and I'll give feedback as soon as possible in anything that I think we're lacking, but I'm pretty sure, like I said, that we have everything in place to go back to cruising," Meisel said.

Delilah Herrera, another employee volunteer, has been especially eager to get out and onto a ship.

"I'm very healthy, thank God, and just need to get out and see my friends and see my work family."