It's been in the news a bunch of times. "Strategic defense stockpile," I think is its designation.
Pro Publica had an odd tweet saying that some states got their full request (3/11/20 request) and some didn't, quite rage-provoking; and then an article actually trying to figure out why that was so. Just see the tweet, just feel the rage. Read the article and it makes you think a bit more.
20 some warehouses, all hush-hush (to prevent thefts before or during an emergency), with unspecified stuff. But in some cases they've said, things like "12 million N95 masks". The Pro Publica article says what the basica guidelines are for distributing them. 25% to be doled out based on population, 25% on the basis of something else (need? I forget). 50% to be held in reserve for real emergencies. Since they're distributed and should have a quick turnaround time, I'm assuming a "real emergency" isn't "we predict in 10 days we'll run out" but more like "tomorrow we use our last one." But states request them, not hospitals, and the request must be made.