Collins submarine problems.

Sailors aboard a Collins-class submarine forced to return to base for repairs during a multinational exercise near Hawaii last week would have been profoundly disappointed, a former senior submariner says.

It is the second time in just over a year a Collins-class submarine has had to withdraw from a major international exercise because of mechanical issues.

The former commander of the Australian Navy Submarine Group, Steve Davies, said the officers and crew of HMAS Farncomb would have been riding high after successfully sinking a decommissioned United States warship with a Mk 48 torpedo during RIMPAC 2012.

HMAS Farncomb experienced ''a minor flood'' shortly after the firing exercise while snorkelling to recharge its batteries.

One of the hoses in the submarine's weight compensation system split, spraying water into a machinery space.

Emergency measures were invoked with the ship withdrawing from the exercise and returning to Pearl Harbour for repairs.

HMAS Dechaineux was unable to take part in Exercise Bersama Shield last May when issues with her engines left her stranded in Singapore.

Mr Davies, who was in Canberra last week as part of his new role as executive director of the Submarine Institute of Australia, said he had experienced similar disappointments during his own service and could feel for the 60-strong crew.

It was unfortunate the hose failure had drawn attention away from the excellent job HMAS Farncomb had done in sinking the former US ammunition ship, USNS Kilauea, with a single Mk 48 torpedo.

Hitting a target that was dead in the water was far more challenging than locking on to a moving ship.

''Torpedoes like speed,'' he said. ''A moving object is much easier to spot. One of the tactics you can use against a torpedo attack is to stop near a border or boundary of some kind.''

The firing exercise, or SINKEX as it is known, would have been a very costly undertaking.

In addition to missing out on Kilauea's value as scrap, the United States Navy would have also had to spend a lot of money decontaminating the vessel to make sure she was safe to sink. The torpedo alone costs more than $3.5 million.

''The Mk 48 Model 7 has been developed jointly by Australia and the US,'' Mr Davies said.

''It has sonar, guidance and tracking systems and trails a wire.''

The torpedoes, which carry just under 300 kilograms of explosives, are fitted with sophisticated magnetic sensors that allow them to detonate under their targets to inflict the maximum possible damage. They weigh almost 1700 kilograms and are 5.8-metres long.

Classified as a heavy torpedo, the Mk 48s are designed to break a ship in two.