The Royal Navy nuclear submarine HMS Superb hit a rock as it was diving to pass through the northern Red Sea on Monday, causing damage to her main sonar.
None of the 112 crew was injured and all remained on board as the navy considered where the submarine would dock for repairs. It is understood that Superb was 50 miles (80km) south of Suez, having passed through the canal, when it hit "an underwater pinnacle".
A Ministry of Defence spokesman said : "There were no casualties and the submarine remains watertight, is safe on the surface and able to operate under her own power. The submarine’s nuclear reactor is completely unaffected, and there is no environmental impact.
"Notwithstanding this, from the initial assessment on board the submarine, it is clear that there is some damage to her main sonar which prevents her conducting submerged operations, consequently her programme is being reconsidered. No other vessel, military or civil, was involved in the incident."
An investigation was begun immediately and a board of inquiry will look at what led to the collision.