I think the root cause, using tracing paper to prevent the charts from being defaced and thus save a couple of quid, is typical of the "penny pinching" attutude our Armed Forces have been forced to adopt because of Brown's unwillingness to fund them properly.

LOL, Typical...

It appears the incident happened in 2002. From the North West Evening News:

A BARROW-BUILT submarine needed £5m of repairs after it ran into the sea bed at 15 miles an hour during a badly supervised training exercise for potential sub commanders.
A0146630
DAMAGED: HMS Trafalgar which run aground while taking part in a military exercise, in November, 2002, needed £5m worth of repairs ministry of defence

Two officers were court martialled and given a reprimand after the 2002 incident aboard HMS Trafalgar, the sub named after the famous naval battle won by Lord Nelson.

Details of the undersea prang were obtained by The Times newspaper under the Freedom of Information Act.

It was caused by basic navigational errors made during a training exercise for three "students" on board who were learning to be submarine commanders.

Tracing paper over the submarine's chart also covered vital information, including the tide at tidal stream at that point off the Isle of Skye.

Full article here