"If you're trying to get someone who's sick with a fever off of a submarine and it's cold and raining outside, the only way in and out of a submarine, generally, is through a fairly narrow hatch"

This quote is referring to the trouble of getting somebody who is sick with a fever off of a submarine. The speaker is stressing the challenge of the task by noting that it is cold and raining outdoors, and that the only way in and out of a submarine is through a relatively narrow hatch. This implies that the individual should be thoroughly and gradually moved through the hatch, which can be hard and time consuming. The speaker is likely trying to stress the trouble of the job, and the value of taking the required safety measures to make sure the security of the individual being moved. The speaker is also likely trying to emphasize the value of having the right devices and workers to aid with the job.