Mr Coaker made the claim as he visited Rosyth shipyard to meet staff working on the Royal Navy’s aircraft carriers, and hear their views about independence.
The Labour MP warned that a Yes vote would mean the UK would no longer order warships from Scottish shipyards, with all future contracts handed to firms south of the Border.
He said: “The jobs of thousands of Scots in our defence industry are secured by being part of the UK.
“One thing we know beyond doubt is that leaving the UK would cost defence jobs.
“The UK Government has never awarded a contract for complex warships outside of the UK. The idea that somehow everything would carry on as it is just because Alex Salmond says so simply isn’t credible.”
SNP defence spokesman Angus Robertson said: “It is beyond belief Scottish Labour are claiming shipbuilding is safer in Westminster’s hands. The UK track record on defence in Scotland is appalling, with a multibillion-pound defence under-spend and the loss of more than 11,000 jobs in the last decade.”