In a bid to reassure South Australian voters the Coalition government will deliver on jobs, Prime Minister Tony Abbott this week promised to secure 2,500 shipbuilding positions by 2020.

In Adelaide for a three-day Cabinet meeting, Mr Abbott said the jobs would be “for all time, as a result of the decisions the government is now taking”.

The plan involves bringing forward two major defence construction projects – the construction of new offshore patrol vessels to start in 2018 and new naval frigates in 2020 – estimated to be worth $39 billion.

A next-generation submarine fleet worth $50 billion is also on the Coalition’s agenda, but faces a competitive tender process to include Japanese, French and German shipbuilders.

With SA experiencing the country’s highest unemployment at 8.2 per cent, the PM emphasised the frigate project was the “first prize” for the state, while future submarine jobs could be the next “prize”.

The announcement didn’t come short of critics. With the Coalition facing local anger at reneging on a promise to award the Future Submarines contract to SA, Labor leader Bill Shorten said the defence contracts were merely “political prizes aimed at just saving [Mr Abbott’s] own job”.

SA Senator Nick Xenophon suggested people should beware of the prime minister’s track record and called the announcement “alarmingly short on detail”.

“How is this promise – to build the future frigates in SA – any different from the Coalition’s 2013 promise to build 12 submarines in SA?” said Senator Xenophon.

“The government cannot expect Australians to believe it on the frigates, until it delivers on its promise to build the $50 billion submarines in South Australia. This promised frigate build is at least two elections away. If one week is a long time in politics, then two election cycles is an eternity.”

Meanwhile, another senior SA parliamentarian of Hellenic descent, not always known for his support of the Abbott government, took to Twitter to register his enthusiasm for the multi-billion dollar project.

SA Treasurer Tom Koutsantonis tweeted: “Credit where credit is due. Congratulations to PM Tony Abbott on his decision on naval shipbuilding in Adelaide. Great for SA.”