More than 100 contractor jobs have been axed from ASC in Adelaide today as the shipbuilder works to become more "efficient".

Australian Manufacturing Workers' Union SA assistant secretary Colin Fenney said the 101 contractors included fabricators, boilermakers and pipefitters who were employed on the Air Warfare Destroyer Project.

Another 120 contractors lost their jobs in May.

Mr Fenney said the Federal Government was "clearly to blame" because of its failure to take the option to build a fourth Air Warfare Destroyer (AWD) as outlined in the 2013 Defence white paper.

"These workers are victims of the Federal Government's failure to recognise the need for a continuous building program to maintain our shipbuilding capability," he said.

"[Prime Minister] Tony Abbott claims he's going to create 500 shipbuilding jobs in Adelaide but unless new orders are placed soon, the jobs of thousands of workers already in the industry will be at risk."

The first of three AWDs being built by the ASC, formerly known as the Australian Submarine Corporation, was floated in Adelaide in May, despite being due for delivery in 2014.

The Federal Government claimed the cost for the three ships on order had blown out to about $9 billion and criticised the shipbuilding company for being inefficient.

An ASC spokeswoman today said the company was making "enhancements to the way it undertakes production activities, including changing the sequencing of work".

"While the change in sequencing will lead to efficiency gains during the entire construction timeline for each ship, it means at this stage of the build, the nature of the work to be performed is incompatible with the level of production, contractors on site and the type of work that is required," she said.

"This contractor management activity is normal practice for projects of this nature and has, and will, occur several times over the life of the project."

Independent Senator for SA Nick Xenophon said the "stop-start" nature of naval ship-building in Australia led to inefficiencies and uncertainty "that damaged Australia's naval shipbuilding capacity.

"It defies credibility for the Federal Government to be critical of the AWD program when its own inaction and dithering is a key contributing factor to any cost premium," he said.

SA Defence Industries Minister Martin Hamilton-Smith said it represented a "perilous" situation facing naval shipbuilding in Australia.

He said the Government was supportive of productivity gains but "consistent job losses underlined" a need for the Federal Government to come up with "a 30-year continuous strategic shipbuilding plan to rescue an industry which is hanging on for survival".

This included building a new fleet of submarines that the Federal Government promised to build in Australia prior to the last election, but once elected, threatened to build overseas and has since put out to tender in a "competitive evaluation process".

"$250 billion worth of naval shipbuilding work is at stake over the next 30 years," Mr Hamilton-Smith said.

"Economic modelling shows that there are 120,000 man-years of work at risk if the Federal Government decides to send the submarine build overseas.

"Our next generation of submarines and future frigates must be built in Australia, by Australian workers, to defend Australia."

South Australia last month hit a 15-year high for unemployment, rising to 8.2 per cent, the highest in the nation.

Australian Bureau of Statistics showed that 2,000 people lost their jobs in regional SA alone during the month of June.

"It's even more important now that the Federal Government make investments in the future," Mr Hamilton-Smith said.

"What do they want going forward? Do they want to be handing out unemployment benefits, or do they want to be rewarding workers with jobs?"