Neither major political party questioned the need for the future submarine project; they feared voters would see them as soft on national security.

Our first new "attack-class" sub is due to enter service about 2035. The construction of the rest of the fleet will probably extend to 2050. The subs should remain in service until the 2070s.

The Shortfin Barracuda will displace 4500 tonnes (surfaced), measure 97 metres long, have an 8.8-metre beam, use pump-jet propulsion, have a range of 18,000 nautical miles, a top speed greater than 20 knots, an endurance of 80 days and a crew of 60.

The Collins class, which it is replacing, was the first diesel-electric submarine specifically designed for Australian conditions – notably long transit distances and diverse sea states. The Collins was an original design with inherent noise problems. There was no evolved design concept to replace it.

The preferred options to replace the Collins class were to rework it or buy an existing submarine design and modify it for Australian conditions. The government opted for the latter, and chose a conventionally powered variant of the French Barracuda-class nuclear-powered sub.

Some commentators asked: "Given our requirements, why not just go for a couple of nuclear-powered submarines?" Six nations use nuclear-powered submarines: France, the United States, Britain, Russia, China and India. Our close allies France, the US and Britain now only use nuclear-powered subs, while Russia, China and India have mixed fleets. (Nuclear-powered subs are used for long-range, blue-water deployments; conventional vessels are deployed mainly in coastal waters.)

The Australian government ruled out nuclear propulsion because of: our lack of an indigenous nuclear industry; concerns about maintenance dependence and sovereignty issues if we bought or leased a nuclear-powered sub; and likely public opposition to nuclear technology.

So the Royal Australian Navy was not given the option of considering nuclear power. It would, however, have been cheaper and more practical, because we could have bought a proven nuclear-powered vessel (such as the US Virginia class), without the need to modify it, for about $4 billion each. (Virginia-class subs are designed for a broad range of open-ocean and shallow, coastal-water missions.)

Because the government delayed its decision and did not choose an "off-the-shelf" option, Australia's Collins-class subs will require a "life of type" 10-year extension so they last until the mid-2030s.

The Defence Department and the military can argue, with reasonable justification, that we don't know what the strategic environment will be like in the lifetime of major weapons platforms (to the 2070s, in the case of our future subs) and we can't afford to be caught short.

Submarines were certainly devastating weapons in past conflicts. German U-boats in both World Wars were very effective in enforcing blockades against enemy shipping. During the Falklands war in 1982, the sinking of Argentine cruiser Belgrano by British nuclear-powered submarine HMS Conqueror effectively kept the Argentine navy out of the conflict.

We could be caught short, though, as new technologies become available that make long lead-time platforms more vulnerable – even redundant. Large warships in particular will be at risk in future decades, which is an argument for smaller, more capable, stealthy surface vessels or submersibles (not new destroyers). But you can't convince navies that bigger isn't better.

One important underwater development is unmanned underwater vehicles (or UUVs). They can be divided into two categories: those controlled by a remote human, and autonomous vehicles that operate independently of human input.

The current technical challenges facing these drone subs include endurance (due to limits on power sources) and command-and-control at extended ranges. Once these challenges are overcome, military UUVs (like drone aircraft) will provide significant advantages over manned systems.

In the interim, some hybrid systems will enter service. Russia is reportedly developing a submarine-mounted variant of its Poseidon drone sub that will be able carry a nuclear warhead; it could be deployed in the late 2020s. The intent would be to explode the warhead underwater near a coastal city, creating a tsunami to destroy the city.

Two Poseidon-carrying submarines are expected to enter service with Russia's Pacific fleet. Each submarine would carry up to eight drone subs. Their primary aim would be to deter a US attack, but their deployment in the Pacific will concern allies with major coastal cities, such as Sydney.

China's "912 project" aims to develop a new autonomous drone-sub capability to mark the Chinese Communist Party's centenary in 2021. The project is said to be a countermeasure to the US Navy's development of long-range, extra-large drone subs. China's first-generation drone subs will reportedly be able to lay mines and conduct surveillance.

In the future, drone subs could have a variety of purposes: launch attacks – while on the move or from long-term "sleeper" positions – against land targets, enemy submarines and surface ships; lay mines; place seabed sensors; surveillance and reconnaissance; gather intelligence; and so on.

They will be much cheaper to build and operate than manned submarines, and without the crewing challenges. Collins-class submarines now have 58 crew members, but we have never been able to raise more than four crews for our six submarines. (The US Navy has duplicate crews for its operational vessels so that it can deploy them for protracted periods.)

Past measures to try to improve our navy's crewing included: increasing each sub's complement to spread the workload; having mixed crews; reducing the length of patrols; increasing shore leave; paying bonuses to submariners; and providing internet access on-board. Some of these measures reduced the submarines' effectiveness.

There is little point in having next-generation submarines that can stay at sea for 80 days if sailors aren't prepared to be away from home that long – or can't exist without regular internet or smartphone access. Assuming these crewing problems continue, it's likely our new subs will spend most of their time in port.

And if our subs become more vulnerable to enemy action in future, as seems inevitable, that will presumably make it even harder to recruit submariners.

For all of these reasons, it was extravagant and foolhardy to commit ourselves to a $50 billion program for 12 modified diesel-electric submarines over a 30-year time frame. But the program will create Australian jobs and, of course, a federal election is on the horizon.

Clive Williams is a visiting professor at the ANU's centre for military and security law, and an adjunct professor at ADFA. clive.williams@anu.edu.au