It was fascinating when the topic came up. I just always assumed we had idle capacity ready to go. That is why we spend so much to have that capacity.

It turns out that we just spend a lot but don’t have extra capacity.

Here is just one of the many articles on it.

https://www.businessinsider.com/pentagon-increasing-production-of-155mm-artillery-shells-2023-1

Currently, the US produces just over 14,000 rounds of 155mm ammunition every month. As The Washington Post reported last month, Ukrainian forces have previously fired that many rounds in the span of 48 hours.