World's biggest hospital ship

Kingston, Jamaica (CNN)With more than 700 medical personnel, 5,000 units of blood and 12 operating rooms, it is one of the largest trauma facilities in the United States. What sets it apart from most others is that it just happens to float.

This is the USNS Comfort, which, along with its sister ship, the Mercy, is the largest hospital ship in the world. The twin ships are actually oil tankers-turned-floating hospitals -- each the height of a 10-story building and the length of three football fields.

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The Comfort recently docked in Jamaica as part of a humanitarian mission called Continuing Promise, which will see it sail around South and Central America, and the Caribbean. Jamaica was the third of 11 stops that will take place over the next five months, during which time the staff aboard the ship will care for more than 100,000 patients.

Captain Christine Sears is a urologist and the chief medical officer for this mission -- her first aboard the Comfort.

"One on one as a surgeon you can help one person as a time, and that's very dramatic and very fulfilling," she said. "(But) being able to reach more people ... is such a blessing, to be able to lead and help more people."

As well as performing surgeries on the ship, the crew set up temporary medical sites on shore, with the Comfort carrying all the medical supplies needed. Each country gets roughly 30-40 pallets of supplies and whatever is left over is donated to the host nation. This massive undertaking is funded by the U.S. government at a projected cost of $40 million, while NGOs also donate money, supplies and volunteer time.

"It's part of our overall military strategy," explained Captain Sam Hancock. He's been in the U.S. Navy for almost 25 years -- but a mission like this is a first for him.

"The partner-nation building, working to develop the relationships with the countries in this region and with the personnel, whether the ministries of health and everything that we work with coming into each country ... the relationships that are established will pay dividends in the future," he said.

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It's a massive effort on all fronts, but a hospital ship needs more than just doctors, nurses and medical staff; the Comfort is a fully operational vessel, with engineers, a flight crew, cleaning staff, and a kitchen where chefs have 1,000 mouths to feed, three times a day.

Medical stations

In Jamaica the Comfort's medics left the ship to set up medical stations in gymnasiums and existing clinics, providing services including pediatric care, women's health, cardiology, eye exams, general surgery, dentistry and everything in between.

Among the Comfort's patients was Marleen Maxwell. She's 56 years old, from Kingston, Jamaica, and for eight years she's been living with an overactive thyroid -- a gland near your windpipe that produces hormones to help keep your body in check.

"It hurts ... and sometimes you feel it come up like it blocks the airway," said Maxwell. She says the healthcare in Jamaica is good if you can get it, but she's been waiting three years for surgery.

So Maxwell went aboard the Comfort to have her enlarged thyroid removed. Her nurse was lieutenant junior-grade Kimberly Stoops. Aged 27, it was her first deployment with the Comfort, and she did her best to put her patients at ease.

"I know it's scary for a lot of these patients coming onto a ship that they're not familiar with," she said. "A hospital in general is scary, but then coming somewhere where it's not your territory and then seeing people in uniform can be daunting, so I try to break down those borders and introduce my name and ask if they have any questions, try to explain things thoroughly before I do them, so that I don't catch them off guard."

Mixed emotions

But it can be tough to be away from home on a long mission.

"It's hard to be away but it's also great ... knowing that we're doing really good work here," said Stoops. "A lot of mixed emotions -- you have those days where you really miss home and then you come in and see someone's smiling face like Marleen and just so much you can do, and it really brings you up again."

A big part of the Comfort's mission was helping to train Jamaican medics. First assist on Maxwell's operation was Dr Natalie Wylie, an ear-nose-and-throat surgeon and head of the Kingston public hospital. For her, the Comfort was a most welcome visitor to local shores. "I think the whole of Jamaica welcomes the Comfort," she said. "If they could see more patients, if they could do more surgeries, if they could stay longer, if they could leave the ship with us," she joked.

The operation took several hours but it went well, and Maxwell returned home the next day. Jamaican doctors helped with the operation, and they continued with her follow-up care.

As she recovers, the Comfort will continue on its mission, with stops in Nicaragua, Panama, Colombia, El Salvador, and many more. It's a remarkable example of what a highly-trained hospital staff can do -- even on the high seas.