Following on from the 'medical theme' in relation to females serving on Submarines, the following quote was taken from a recent US interview with Elaine Donnelly, president of the Center for Military Readiness by CNSNews.com. Same would apply to UK boats who spend the same amout of time at sea as there US counterparts.
Quote as follows: "Medical emergencies occur at two-and-a-half times the rate among women than they do among men, and a large percentage are due to pregnancy. If you create that kind of a situation, you shouldn't be surprised if the entire mission of the submarine is compromised. It's not a woman's issue, it's a national security issue. To say that men are just as susceptible to medical emergencies, as in the case of emergency appendicitis, for example, doesn't wash. I asked the Navy how many cases of appendicitis we've had, among either men or women, in the last three years. It's very rare. Pregnancies on the other hand are extremely common."
The last think you want is to be on a global patrol, somewhere under the arctic ice-pack to then face a situation where one of your female crew has morning sickness!