Besides the Emigration and Immigration events when migrating between countries, I have created Port of Departure, Port of Transit and Port of Arrival for non immigration events. Additionally, I have found Ocean Cruise for a few records when a relative departed and returned to the same port.
One example of how I do something for a person’s military career, is to have a list of Military Service events with the Description detailing things like Enlistment, Basic Training, Duty Station, Deployment, etc. While not sub events, it does present a nice list for the person.
Here is a post from another thread you may find of interest…