Australia's new nuclear-powered subs will take decades to arrive, but they'll put it in a very exclusive military club

• The US, UK, and Australia recently announced a pact meant to boost their militaries' ties and capabilities.
• A central part of the pact is the US and UK's pledge to help Australia acquire nuclear-powered subs.

In September, Australia, the UK, and the US announced a trilateral security pact aimed at strengthening their defense ties. Their leaders stressed that it wasn't aimed at another country, but it is widely viewed as a means to counter China.

The central component of that pact is the sharing of high-end technology and cooperation on weapon development and procurement. What stood out, though, was the US and UK's pledge to help Australia acquire eight nuclear-powered submarines.

The move is historic. The US has only shared nuclear-propulsion technology once - with the UK in 1958. It will also put Australia in a very exclusive military club.

Only six other countries operate nuclear-powered subs. The US, UK, France, India, Russia, and China have built up their fleets for decades, and they now include a number of classes with distinct missions.

Nuclear-powered ballistic-missile subs

The largest and most feared submarines today are nuclear-powered ballistic-missile subs, classified as SSBNs.

They can sail deeper and faster than conventionally powered subs. They also carry large nuclear payloads and remain submerged for months - making them effective second-strike weapons.

The US, UK, France, and India each operate a single class of SSBN.

The US Navy's 14 Ohio-class SSBNs can carry 24 submarine-launched ballistic missiles (SLBMs), while the Royal Navy's four Vanguard-class can carry 16.

Both navies use the Trident II SLBM. Each Trident II has a range of 4,600 miles and can carry multiple independently targetable reentry vehicles (MIRVs), which substantially increase the number of warheads on each missile.

The French navy's four Triomphant-class boats carry 16 M45 or M51 SLBMs, which can carry up to six and 10 MIRVs, respectively. The M45's range is about 3,700 miles and the M51's is 4,900 miles.

India's Arihant-class has four silos capable of launching either 12 K-15 short-range SLBMs or eight medium-range K-4 SLBMs. The K-15 has a range of 460 miles, while the K-4 has a range of 2,170 miles.

India plans to have a total of four Arihant SSBNs by 2030. One is in service, and the second is set for commissioning next year.

China's four Type 094-class boats can carry 12 JL-2 SLBMs. Each of those missiles can carry three to eight MIRVs and are believed to have a range between 4,500 to 5,500 miles. Two more Type 094s are under construction, the US Defense Department said in 2020. China also has an older Type 092 SSBN, though it is likely only used for testing.

Russia's navy has the most diverse SSBN fleet: one Typhoon-class, one Delta III-class, six Delta IVs, and four of the new Borei-class.

Each Borei-class sub can fire 16 RSM-56 Bulava SLBMs, which can carry up to 10 MIRVS and are believed to have a roughly 5,000-mile range. Russia plans to have 10 Boreis in service by the end of the decade.

Nuclear-powered attack and cruise-missile subs

Nuclear-powered attack and cruise-missile submarines - designated SSN and SSGN, respectively - can't carry ballistic missiles, but they are equally important.

SSNs can hunt and kill enemy ships and submarines, and both types can attack targets deep inland with cruise missiles.

The US Navy operates three types of SSN: the Los Angeles, Seawolf, and Virginia classes.

The Los Angeles class is the oldest, and 28 are still active. They have four torpedo tubes, and later versions are fitted with 12 vertical launch systems (VLS) for cruise missiles.

The Seawolf class was developed at the end of the Cold War and is designed for sensitive missions. It is also heavily armed, carrying up to 50 torpedoes or cruise missiles it can fire from its eight torpedo tubes.

The Virginia class is the newest, and 19 are now active. They have four torpedo tubes and 12 VLS tubes for 37 torpedo-sized weapons. Future Block V Virginias will have even more VLS tubes, increasing their armament to 65 torpedo-sized weapons.

Four of the US Navy's Ohio-class SSBNs were converted into SSGNs in the 2000s. Each can now carry as many as 154 cruise missiles.

The Royal Navy's two Trafalgar-class attack subs have five torpedo tubes, while newer Astute-class boats, of which there are four, have six tubes. Both can fire torpedoes and cruise missiles and can carry 30 and 38 torpedo-size weapons, respectively.

France's five Rubis-class and single Suffren-class SSNs also rely on their torpedo tubes - four and eight of them, respectively - to launch torpedoes and missiles.

China's six Type 093-class SSNs each have six tubes capable of firing torpedoes and cruise missiles. They are regarded as China's most powerful attack submarines, and some may now be equipped with VLS tubes.

Like its SSBN fleet, Russia's SSN and SSGN fleet is large and diverse, comprising two Sierra-class, three Victor III-class, and 10 Akula-class SSNs, as well as eight Oscar II-class and two Yasen-class SSGNs.

In 2019, India agreed to lease one of Russia's Akula-class SSNs for $3 billion. It will be the third Russian SSN leased by India and is expected to be delivered by 2026.

Australia's nuclear sub

Australia's future nuclear-powered subs won't be SSBNs, but not much else is known about them.

Australia may select one of the existing American or British designs - most likely of the Virginia class or the Astute class. Adopting an existing design would allow construction to begin relatively soon.

Australia could also wait for the British SSN(R) or American SSN(X) programs to develop and adopt one of those designs, though it will take more than a decade for either of them to hit the water.

Australia may also pursue a totally new, domestically developed design with only technical help from the British and Americans.

Canberra has made clear that it wants most of its future submarines to be built in Australia. This was one reason Australia's sub deal with France fell through.

But it's not known how much of the work the US and UK will cede to Australia, nor is it known if Australia can develop and build such a complicated system domestically. Australia's six Collins-class submarines were designed in Sweden, and some were partially built there.

Regardless of how they are built, the new subs will take a decade or longer. The admiral leading the country's nuclear-powered submarine task force told lawmakers in October that he wants "at least one boat" in the water by 2040.