It was viewed as a saving grace for a developing health crisis in the wake of Hurricane Maria: the USNS Comfort was heading to Puerto Rico to provide much-needed medical care.

But in the two weeks since the U.S. Navy's floating hospital arrived in San Juan, it hasn't proved as helpful as many had hoped, and that's because it's too difficult to get sick patients onto the ship, critics say. As of Tuesday, just 33 of the 250 available beds on the Comfort were being used , according to CNN.com.

"Only patients with critical needs requiring specialized care will be transferred to USNS Comfort," Coast Guard Lt. David Connor told CNN.com in an email.

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FEMA told CNN.com that the Comfort is being used as a last resort at the end of a long line of steps that must be taken first with patients. They must first go to a local medical facility, then to the medical coordinating center in San Juan. From there, they might be sent to Humacao, where the Army's Combat Support Hospital is located. After that, a patient could be sent to the Comfort.

"USNS Comfort has treated over 100 patients to date, conducting logistics and medical support operations in Arecibo and Aguadilla ," FEMA said in an update posted Tuesday.

One such patient was a woman who gave birth aboard the ship on Saturday – the first birth on the Comfort since 2010, when it was docked off Haiti following a catastrophic earthquake.

"I think the birth of that little girl has reinvigorated the crew ," Capt. Kevin Robinson, the Comfort's mission commander, said in a report released by the Department of Defense.

Puerto Rico Gov. Ricardo Rosselló told CNN.com he has vowed to overhaul the procedure for which patients are admitted onto the Comfort, and hopes they'll move more patients there in the coming days. In the meantime, doctors are waiting for the influx of patients they'd been promised since the ship's arrival on Oct. 3.

"I know that we have capacity," Robinson told CNN.com. "I know that we have the capability to help. What the situation on the ground is ... that's not in my lane to make a decision. Every time that we've been tasked by [Puerto Rico's] medical operation center to respond or bring a patient on, we have responded."