National Australia Bank issued €750 million of covered bonds yesterday - its fifth transaction since the covered bond market opened in Australia last year.A notable feature of the issue was its term: the 12-year term is the longest dated euro covered bond from an Australian issuer.The fixed-rate securities will pay a coupon of 2.25 per cent. The spread of the bonds was set at 33 basis points over mid-swap.NAB said in a statement that the order book had 40 accounts.NAB has issued about A$10 billion of covered bonds since January last year. The bank has used up about 30 per cent of its covered bond limit.