How can a sophisticated nuclear submarine run aground in this fashion?

The accident involving the Trafalgar is a remarkable occurrence given that she is a 'state of the art' vessel.

The submarine is fitted with a Kelvin Hughes Type 1007 navigation radar and also SIX separate sonar systems.

Trafalgar is also fitted with the Submarine Command System (SMCS) developed by the UK Company BAeSEMA, which features an integrated suite of tactical picture, weapon management and fire-control functions supported by oceanography, onboard training and navigation facilities.

HMS Trafalgar had an escort at the time. Shouldn't the surface vessel have sent a warning?

The surface escorts would obviously send a warning if they felt the submarine was at risk.

The Trafalgar's sonar and navigation equipment should have been able to provide ample warning.

I think we will have to wait for the investigation before we can account for the actions of the surface vessels in this case.

The Navy say there was no damage to the "pressure hull". What is the pressure hull?

The pressure hull acts as an inner hull within the outer shell of the submarine.

It equalises the air pressure within the submarine according to its depth.

Regulation of internal pressure is essential to ensure comfortable conditions for the crew and also to prevent the submarine from imploding due to the external water pressure.

There were two crew members injured in the incident. Presumably there was potential for quite serious injury in these circumstances?

Potentially, yes. The casualties were light because the submarine only struck a glancing blow.

A heavier type of collision is extremely unlikely given the ship's sophisticated navigation equipment.

Does the submarine commander face an automatic court-martial over this?

No - a court-martial is a possibility but only after an internal investigation, which is likely to take some time.

HMS Nottingham suffered severe damage in the Tasman Sea earlier this year. These incidents must be pretty embarrassing for the Navy?

Yes, and the situation is exacerbated by the tight financial constraints under which the Navy operates.

Initial estimates suggest that the repair work on HMS Nottingham could cost as much as �50m.

The damage to Nottingham is such that the Navy is unsure whether repairs to the ship will be cost effective given that it is scheduled to be taken out of service in 2012.