From the dark days when the Navy was hard-pressed to sustain a single operational Collins submarine, it's now able to keep two and often three at sea while others undergo maintenance.
In the latest report card on Collins sustainment, UK submarine expert John Coles said few would have predicted the performance of the six Collins subs would graduate from mediocre to excellent in less than four years at almost level funding.
"If there were unit citation medals to be awarded, the Submarine Enterprise would surely qualify," he said in the report.
Collins availability would have been even better if not for a fire aboard HMAS Waller in February 2014. The sub didn't rejoin the fleet until mid-2016.
The latest review found two submarines were available for operations more than 90 per cent of the time, three for more than 50 per cent and four occasionally since January 2014.
Now that HMAS Farncomb has completed full-cycle docking - two years of top to bottom maintenance - four boat availability is expected to increase.
Previously full cycle docking took three to four years and was conducted every eight years. Now that's done for two years every 10 years.
In the 2012 review, Mr Coles compared Collins maintenance against international benchmarks for diesel electric submarines, finding Collins was wanting in key areas.
Now it's approaching or exceeding those benchmarks. Days lost due to defects is now a quarter what it was while maintenance overrun days is a fifth.
Submarine availability days are now more than 85 per cent of the international benchmark, up from 56 per cent.
Mr Coles said Collins availability should reach or better the international benchmark in the next 12 months.
"For the Submarine Enterprise to reach this level of performance is a significant achievement that has not received the attention that it merits," he said.
Defence Minister Marise Payne said submarines played a key part in national security.
"Improvements to the availability and reliability of the Collins Class submarines means that they can spend more days at sea conducting exercises and operations that directly contribute to our strategic defence capability," she said in a statement.
