When is peacetime damage to a submarine major?

HMCS Corner Brook suffered a grounding accident on June 4, 2011. The sub surfaced and returned to port under her own power. 

Tim Dunne, wrote “Journalists sub-par on sub debate” on March 3, 2012 in the Halifax, Nova Scotia, Canada, Chronicle Herald. Here is part:

"When New York Times writer Paul Krugman observed, "The people who talk the most understand the least," he could easily have been thinking about some Canadian television reporters and commentators as they breathlessly told of the damage to the submarine HMCS Corner Brook.

The boat struck bottom in 45 metres of water near Nootka Sound on western Vancouver Island, June 4 of last year, cutting a four-by-five-metre hole in the boat’s front. CBC TV News showed "exclusive" photographs and alluded to efforts by the Royal Canadian Navy to covertly raise the vessel out of the water "under cover of darkness."

...Missing from the debate was that the damage was to the front of the submarine’s fibreglass casing. Four metres inside the damaged casing is the pressure hull, made of 3.8-centimetre HY 80 steel, and this is the main compartment where the crew and controls are located. While the vessel is in the water, the space between the casing and the pressure hull is flooded.

The special high yield (HY) steel alloy is designed to military specification to allow submarines to withstand the pressures of deep dives. This special steel has a yield stress of 80,000 pounds per square inch, corresponding to a depth of about 1,800 feet. While the casing was damaged, the pressure hull, able to withstand incredible stresses, was untouched.

There have been questions about why the navy took the ship out of the water at 4 a.m., "under cover of darkness." The RCN’s deputy commander, Rear-Admiral Mark Norman, explained that the 3,500-tonne submarine was raised out of the water on the navy’s syncrolift, timed to take advantage of high tide and to minimize water turbulence from other vessel traffic in the harbour.

... HMCS Corner Brook’s grounding should not be trivialized. It was a serious incident and had the potential to be a tragedy. However, commentators should not overstate the accident and ignore the important contributions which Canada’s submarines make to training, sovereignty and prevention of drug trafficking...” see WHOLE CANADIAN ARTICLE

Wikipedia advises "On 4 June 2011, Corner Brook while diving off the coast of British Columbia slammed into the seafloor at 5.9 knots (11 km/h) at a depth of 45 metres (148 ft). Two sailors were injured in the collision and the submarine suffered significant damage, with a 2-metre (6 ft 7 in) hole in the bow. Two torpedo tube doors were torn off in the collision.^[25] The submarine surfaced and made port without requiring aid.^[10] The commander of the submarine was later stripped of his command following a board of inquiry.^[26] Repairs and a major refit will keep the sub out of operational service until 2017.^[27] 

Pete