During the episode, some of the nurses are having romantic flings with some of the enlisted crew members. In particular, Nurse Crandall (the pretty blonde) is hooking up with Yeoman Hunkell.
At the end of the episode, the sub's captain is lecturing the crew (probably about "being professional"), the scene takes place on the mess decks. The crew are all seated at a table, with the nurses on one side & the guys on the other. Crandall & Hunkell are directly across from each other, on the opposite end of the table from where the captain is standing. As the captain is talking, the two of them give each other a knowing smile. The scene then cuts to underneath the table. She quietly slips her left foot out of its shoe and proceeds to rub his ankle with her stocking foot. The scene freezes there, as the end credits roll. She is probably wearing suntan nylons.