[LT Guppy]

I mean, you'll be assigned to a ship, but they are in port for months at a time. In port, you'll be doing maintenance, training, preparing for inspections, and inspections.
Each ship had a life cycle (roughly two years long depending on the type of ship) where you're doing maintenance/upgrades, then inspections to qualify for deployment, work ups preparing for deployment, and then finally deployment.
While a ship is in homeport, it will get underway (go to sea) periodically for a couple weeks at a time.