The National Australian Bank has once again shown itself to be the most trouble-prone of all our financial groups, especially where the US is involved, by revealing another $830 million in provisions against dodgy collateralised debt obligations, or CDOs.

The NAB is now the largest mainstream financial group to be caught up in the still imploding US subprime mess. Until now, the damage has been done to a group of hedge funds (such as Basis Capital) and smaller investments by other groups.

According to NAB, the damage was done in the last two weeks as the two big quasi US Government sponsored mortgage groups, Fannie Mae and Freddie Mac, staggered towards possible implosion, only to be supported by the US Government.

It has now made provisions totalling more than $1 billion against the dodgy US securities, meaning that the NAB has provided 90% of the $1.2 billion worth of dodgy securities

The news shocked the market, and NAB shares plunged more than 13% to a low of $26.81, before bouncing slightly to be off 10% at $27.50 just before 11.30 am.

In a presentation to the market the NAB explained its news, the bank revealed:

Rapid deterioration in US residential property markets; NAB conduits include A$1.2bn CDOs with US RMBS assets ; Recent developments point to much higher probability of loss;$830m additional provision quarantines effect but loss mitigation efforts continue; Dividend unaffected and capital position remains strong

[There has been] a rapid increase in past due/defaulted mortgages; Large unsold property overhang and rising due to increasing foreclosures; Security realisations now as low as 50% of mortgage balance; Weakness of monoline insurers increasing likelihood that CDO noteholders will change their behaviour and opt to liquidate.

What upset the market was that this update came two weeks after the bank warned of a possible increase in its provisions against the CDOs.

Since that time the economic environment has deteriorated further. These exposures are being actively managed to minimise the potential for loss. However, notwithstanding that these CDOs are currently meeting all principal and interest obligations, there continues to be a risk that further provisioning may be required.

It was devastating news from the bank, which has been criticised for buying the Great Western bank in the US Midwest rural late last year. It has had an unhappy track record in the US. Remember that in the late 90s and early years of this decade, NAB lost the best part of $3 billion on the Homeside misadventure.

Up to now, it had been thought that Australian banks had escaped the subprime mess, but that’s no longer the case. The irony is that if you’d asked most Australian investment analysts who would be the Australian bank with potential exposure to the subprime mess, the NAB would not have been first choice: Macquarie Bank and Babcock and Brown would have been most picks.

The NAB of course got into trouble in 2004 with $360 million of foreign options trading losses. That saw the bank all but taken into the hands of the key regulator, APRA, and management and the board shaken up.

John Stewart was recruited to takeover as CEO and his reign has now been tainted.