250 NSM doesnt sound like much? How many ships are we going to need to sink?
I would have a view that we would use ammunition in a conflict way faster than people think.
My assessment of conflicts like Ukraine, indicates that peacetime ammunition production (where we are today) is about one- two orders of magnitude less than it needs to be. So when we think we need 10 missiles, we actually need 100-1,000.
If for instance a Hobart were to engage a single enemy combatant, it would likely fire all eight NSM missiles (it's entire magazine) at once, in the hope that one might get through. If it had an LOCSV in tow, it would likely launch what it had too. Call it 16 NSM missiles in a volley.
In defence (flip the picture), the Hobart would need to shield against something similar from the other ship. Standard practice with ESSM/SM2 is to fire two shots per incomming missile. So for 16 incomming, it would launch 32. Perhaps it would need a further 4-8 for anything that got through the initial screen (call these RAM).
So a single hot confrontation (two ships, 1 on 1) could potentially expend 50 strike and defence missiles per ship, (likely within a few minutes). Possibly for no outcome, with both ships sailing away with their original paint afterwards to reload.
How do you break this outcome. Volume. Add a buddy (say a GPF) for a second strike, or carry more strike missiles yourself (second or third LOCSV), or launch something from shore or air (say six F35s with 2 JSMs each, and another four armed with AMRAAMs for protection). So now that 50 missiles in a single confrontation becomes 100 or 150 in a multiple attack scenario, with 30-50 of those being strike missiles (NSM/JSM).
Maybe in this outcome a couple of ships got destroyed or heavily damaged. To achieve that, a very large portion of ammunition inventory got written off, and something like $200-300 million expended on a spectacular fireworks show. On a small battle. That 250 missiles in the cupboard gets depleted fairly rapidly following more than a couple of such confrontations.
In a major war, there might be a dozen or more such scenarios happening simultaneously over the region with allied ships, consuming thousands of missiles in a few days/weeks. They will need immediate replenishment and our allies will look to us to support this.
So, in my view, an in country war stock of NSMs is more like 2,500 units, and a production rate that can be accelerated to around 1,000 per annum to keep up with consumption.