You'd be surprised.
Aircraft that are designated as secret are typically just prototypes that aren't ready for real world combat like the silent helicopters they used in the Bin Laden raid.
Pretty cool idea. Not very effective.
It's surprising what technology people actually think the government has though. Like they have a secret army of scientists making laser rifles and plasma grenades or something.
Truth is its way cheaper and more effective to invest in one or two new models of jets or helicopters and spend the rest of the money on upgrades for them. It's way easier and they don't have to restock their inventory from scratch every decade. Hell we've been using F-15's since the 80's and Chinooks since the 60's.