As the government considers abandoning plans to build its next generation of submarines in Adelaide, there is much for it to consider — operational factors, security issues, intensifying budget headaches, perhaps even what remains of its reputation for keeping its promises.

But among the most telling factor is one that’s notable for its absence — an especially strong concern on the Coalition’s part for its electoral standing in South Australia.

The loss of the Collins submarine project would be a serious psychological blow to the state as it continues to grapple with its declining manufacturing sector, which went from employing over 100,000 South Australians in 1981 to 74,000 in 2011, a period in which the population grew by a quarter.

The decline has been symbolised by the car industry, which received the final nail in its coffin at the end of last year when Holden announced it was ceasing production.

The perceived need to cover the loss has been a major consideration in the policies that have brought about South Australia’s accumulation of defence industries. As such, there has been grave alarm in the state over what is popularly known as the “valley of death” — the dearth of new projects to tide shipbuilding over between the completion of the air warfare destroyer, scheduled for 2019, and the start of submarine construction.

In this environment, pulling the rug out from under the Collins program would appear to be a courageous move. That this might not actually be the case has a lot to do with the depressing question of marginal seats, of which South Australia has precious few.

With the exception of Tasmania, no state swung more forcefully to the Liberals at last year’s federal election. However, all the party had to show for it was the western suburbs seat of Hindmarsh, where the biggest swing in the state was just sufficient to get its candidate over the line.

Three seats that had been won by John Howard in 2004 — Wakefield on Adelaide’s northern edge, Kingston in its south, and Makin in the inner north-east — remained in the Labor column.

All three had been gained on Kevin Rudd’s watch in 2007 and bolted down with big swings at the 2010 election, when Julia Gillard’s home state took a uniquely favourable view of her. The correction in 2013 was not of such scale as to seriously threaten them, with Labor’s winning margins ranging from 3.5% in Wakefield to 9.7% in Kingston. The areas covered by these seats have proved equally sticky at the last two state elections, playing no small part in re-electing Labor from a minority of the statewide two-party vote.

Together with the safe Labor seat of Port Adelaide, home to the ASC’s (formerly the Australian Submarine Corporation) shipyard at Osborne, the three seats are also noteworthy for housing the bulk of Adelaide’s manufacturing workforce.

While these seats loomed large in electoral calculations during the Howard years, it’s hard to see any future path to victory for Tony Abbott running through them. Nor does South Australia appear to present the government with particularly big risks on the downside.

Hindmarsh aside, the Liberals’ most marginal seat in the state is Boothby in Adelaide’s southern suburbs, at which Labor threw everything it had in 2007 and 2010 without quite breaking through. Its failure on the latter occasion was particularly bitter, as it desperately needed gains in South Australia to balance its losses in Queensland and New South Wales.

The cause being lost in 2013, Labor’s energies were thrown into defending what it already held, allowing the Liberal margin in Boothby to blow out to 7.1% — which looks too high a hurdle to clear next time round.

The other theoretically winnable Liberal seat has been Sturt in Adelaide’s inner east, held by none other than Christopher Pyne. Pyne emerged from the 2007 election with less than 1% of his margin intact, but he seems to have found favour with local voters since. He defied the statewide trend of 2010 to increase his margin by 2.5%, then boosted it to double figures in 2013.

With a world to win elsewhere, the Coalition appears to have nothing to lose in South Australia but Hindmarsh — something it could quite happily put down to experience if it were able to hold the line in other states.