At first glance, the government's re-announcement this month of a plan to buy ground-to-ground missiles and their HIMARS launcher vehicles looks like business as usual - wasting more money on equipping the army for land fighting when our pressing military problem is in the air and at sea.

But the acquisition is in fact an important first step towards getting a capability that's relevant to the war we may actually face.

Another missile plan in the same announcement, an order for strike weapons for the navy, was also previously in the works. It amounts to little more than routine updating of equipment.

Thanks to Ukraine's successful use of HIMARS vehicles against Russia, their name has become one of those military terms that have grabbed public attention.

But the HIMARS is just a nifty truck that carries, points and launches missiles; another vehicle model, heavier and less suitable for Australia, can also do the job. Talking about the HIMARS but not its missiles is like talking about an egg carton but not the eggs.

Two types of missile currently go in the HIMARS, and we'll be buying both, the US State Department revealed in May. Both are for attacking ground targets and both are just about useless for facing China.

It's all in the distances they can fly. One is the GMLRS, which can go 70 kilometres. (Don't worry about what these abbreviations stand for; it's always gibberish.)

Six GMLRSs go into each HIMARS. They can be used against such targets as troop concentrations, stationary vehicles, command posts, fuel depots, bridges and so on.

The other missile type is ATACMS, which flies 300 kilometres. It's bigger, so only one fits in each HIMARS. The function is similar.

So these are weapons for land battles, the only thing that the Australian Army apparently wants to think about. Indeed, buying missiles such as these has been in defence planning since at least seven years ago, a time when our military establishment showed little sign of waking up to the China threat.

We are not facing a risk of invasion and are never compelled to send forces to the Middle East, so getting ready for land battles is not our priority. The war that we have to worry about would be one in the Western Pacific that could erupt with a Chinese attempt at seizing Taiwan - or by accident. We'd have to help the US because we'd be terrified that it might lose.

A missile in Australia that flies 300 kilometres against ground targets is obviously irrelevant to fighting in the Western Pacific or even the South China Sea. There would not even be a strong argument for deploying army units with ATACMS missiles closer to the action up there, since they would still have limited value.

But Lockheed Martin and the US Army are developing another missile, PrSM, that will initially fly at least 500 kilometres and later as far as 1000 kilometres. Importantly, they'll adapt it so it can also hit ships.

PrSM isn't very big (two go into each HIMARS) and hopefully won't cost too much.

Now that would be a highly useful weapon for keeping Chinese ships well away from the Australian coast or for threatening targets in the South China Sea from adjacent islands (if we had access to them).

The Coalition government decided in 2021 to pay $70 million to help the US develop the PrSM. There's no doubt that many rounds of that weapon will eventually come into our inventory.

Before that happens, we need to get familiar with operating missiles like it. Our army has never done anything like this before.

So that's the valid reason for buying HIMARS vehicles and an introductory stock of seemingly useless GMLRS and ATACMS missiles. The army can learn the ropes with them.

Next, the US Army is quietly working on missiles that will fly a few thousand kilometres. We should be interested in them, too.

The price will probably be more than $20 million a shot, however, so we're not likely to buy hundreds.

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All these weapons are ballistic missiles, by the way: they're thrown upwards by their rocket motors then fly like balls, coming down very fast.

Meanwhile, the new missile type that the government has ordered for the Royal Australian Navy - a cruise missile, which flies like an aeroplane - is the Kongsberg NSM from Norway.

This acquisition is much less cause for excitement than the new ballistic missile capability, because it will just replace our current anti-ship missile, the Harpoon, which is no longer very good at getting through defences.

So buying NSMs will just rejuvenate a capability that's become unreliable - like buying a new car to replace one you've kept too long.

Destroying ships with missiles depends a lot on giving the target too little time in which to defend itself. One way to do that, used by China, is to shoot extremely fast missiles at the ships. The other, designed into the NSM, is to make the missiles stealthy, so they are already close when the ships detect them.

The NSM is a step forward in being good at hitting ground targets, too, whereas the Harpoon is only so-so at that job. But enemy defences, especially airpower, would have to be pretty weak before an Australian destroyer or frigate would get within 200 kilometres or so from a ground target, which it would have to do to fire NSMs.

Still, the extra capability is helpful. It gives the other side more to be wary of.