Fires, floods, and maintenance delays keep Australia's submarines out of the water as navy begins 'high risk' nuclear transition

Four submarines are meant to be available for service at any point in time — a target the navy's failed to meet for two years. (Image: Nearmap)

The Australian Navy, which is struggling to keep its ageing submarine fleet in the water, had only one battle-ready sub at the start of this year, raising doubts about its ability to run a far more complex nuclear program.

The navy insists its six Collins Class submarines, which this year cost $740 million to run, remain a "lethal capability", but a Four Corners investigation has found it has failed to meet crucial operational targets over the last two years.