I ever readed a story about Vietnam war, which said a soldier want to touch a female reporter's breast before the fight. The reporter was a bit angry at first, but she was moved. Since she heared that the young soldier just do not want to die without feeling the pleasure of sex. Therefore she satisfied the soldier. In the following assault, that soldier is KIA.
The shipgirl is in the same situation as the young soldier. They have no life other than fight, but each of they do want to feel more as a human, as a girl. In somehow, sex might also be the mysterious thing that they want to try. What is more, they might have no chance to meet other male, so the admire become their only possible sex partner. It could be strange that admire is their superior, protector, father and even sex partner, but that is what accurately happen.