I saw and touched Musk's "submarine" which was on display at a science expo in Bangkok I went to a few months ago. It was sort of underwhelming. It was just a metallic tube with some handles on the sides and a thick acrylic removable plate on one end that had a few air fittings screwed into it. I'm sure there was some engineering that went into it. But it certainly did not look like rocket science was involved.