Their world is secretive, often dangerous and at any moment they could be deployed to the farthest corners of the globe to carry out deadly missions.

The men and women who serve on Australia's six Collins-class submarines provide one of the country's most vital pieces of "strategic deterrence" in an increasingly competitive and uncertain neighbourhood.

By the year 2030 the Australian Government is anticipating more than half the world's submarines will be operating in the Indo-Pacific, a maritime environment that is already getting very crowded.

In simple terms submarines provide four crucial roles for the Defence Force: covert surveillance; delivery of special forces personnel, anti-surface ship warfare and anti-submarine attack.

"The real, true capability of a submarine is that I don't have to announce (my) arrival in any place" says Commander Richard Lindsey, the Commanding Officer of HMAS Waller, one of the Collins-class fleet.

Commander Richard Lindsey on the bridge of HMAS Waller. ( Luke Stephenson, ABC )

"If you really want to get down to the baseline, it's about removing that threat, and that's my business".

Commander Lindsey is a veteran of the United Kingdom's nuclear-powered submarines but believes Australia's diesel-electric fleet is world class, and doesn't deserve its "dud-sub" reputation.

"The Collins platform that we see today … is nothing like it was 20 years ago and we need to understand that that platform is improved, and constantly improved throughout," Commander Lindsey says.

In recent weeks HMAS Waller has been taking part in Exercise Ocean Explorer to improve anti-air and anti-submarine warfare, as well as maritime operations aimed at ensuring shipping lanes are clear and safe.

Australian Navy submarine HMAS Waller rises to the surface of the ocean. ( Luke Stephenson, ABC )

This month's war games come against the backdrop of growing concerns over Beijing's military build-up in the South China Sea, and the potential for crucial trading routes to Australia to be cut off.

The increasingly crowded waterways to Australia's north present obvious dangers for any submarine or surface ship but Commander Lindsey insists he is not overly worried.

"Any of those deployments or movements that I make, whether it be around Australia or anywhere else are well planned, well considered and I'm well briefed," he said.

"For me it's just about standard operating: well planned, well supported and making sure that we don't make mistakes."

No personal space, six-hour sleeps and months without sunlight

Operations officer Lieutenant Calvin Timms in the control room of HMAS Waller. ( Luke Stephenson, ABC )

Life as a submariner is full of difficulties and requires extreme resilience but the salaries are usually much higher than other military jobs.

Submariners can typically spend months away at sea, including long periods below the ocean surface without any natural light.

"The biggest challenges of living on a submarine are obviously space," Lieutenant Kaira Wansbury said, the only female crew member of HMAS Waller.

"I sleep, for example, with four of the guys in a small cabin and we only get to sleep six hours a time," the submarine's navigating officer said.

Days on board the submarine can often feel long. ( Supplied: Department of Defence )

Having a cabin is considered a luxury on board a submarine, which can be at sea for up to 70 days at a time and is home to around 60 people.

Junior trainees sleep among the various torpedoes stored at the bottom of the submarine in an area of the boat which also doubles as a makeshift gym.