I recommend to get the process rolling so that you do not need to "remember" to do it later. Have your parents bring or send it after Plebe Summer.
There are many reasons that Mids and yes even a Plebe could need their passport during their time at USNA. Mine needed his Plebe year for spring break and every spring break thereafter!
There are different spring break trips through different organizations/clubs that have out of the USA trips. Glee Clubs, some of the religious clubs do mission trips, the Chaplains offered a trip to Israel last spring break and then their are just groups that do their own thing for spring break that require a passport: cruises (Omega travel (on the yard) usually has a promotion with excellent pricing, ski trips to Canada, diving trips to the Caribbean, to name a few) Summer cruises can also require a passport and for some you do not get an official one - dkred - for that. There is also the opportunity to take a Space A flight to Europe during a leave block - mine did that after youngster year, Opportunities for foreign internships and language schools usually are done on an "official" dkred one. USNA takes care of getting that for you however also holds $$ for returning it to USNA - you don't get to keep it, although it will be given to you upon graduation. When the official one was issued to my son, they changed him $75.00. The $75.00 was credited back to him when it was turned in. It was a surprise when it was given to him just prior to graduation.