In the aftermath of the deadly fire on HMCS Chicoutimi last year, CBC News assigned a team of producers and reporters -- from radio, television and cbc.ca -- to cover the story in-depth. We wanted to know not only what happened, but also how it happened.

The results were almost immediate.

While official reports initially described the fire on board as a “minor” fire, Nancy Durham’s one-on-one interviews with submariners provided evidence that they had never described the mishap as “minor.” Said one submariner: “I mean somebody got (his) wires crossed. Never was it reported from the (sub) that it was a minor fire. I mean it was a major fire. There was no question in our minds, and we were there.” Navy officials would later apologize for having described the fire as less than what it was.

But that wasn’t the only puzzle.

In the days and weeks following the Chicoutimi disaster, Navy spokesmen on both sides of the Atlantic were quick to assure Canadians that the sub was safe. The Navy claimed that it had been refitted to the highest standards. The suggestion was that the fire that killed Lt. Chris Saunders was more likely the result of human error.

The Navy convened a board of inquiry to hear testimony from experts on both sides of the Atlantic. And while the testimony was held in secret, CBC News developed a “deep throat” inside the inquiry. And as CBC developed that and other sources, our investigation of the tragedy cast doubt on both assertions – that the sub was safe and human error was likely to blame. In fact, there were equipment failures on the sub that day, and those failures that led directly to the fire.

The biggest failure was a simple problem: A nut had fallen off a critical air vent between the hatches on the submarine. In the days after the tragedy, captain and crew had borne much criticism for running the sub with both hatches open. After all, the ingress of water into the submarine, and subsequent flooding, led to the short circuit, which caused the deadly fire that claimed the life of Lt. Chris Saunders.

CBC News investigation’ explained for the first time, however, that there was a reason why the hatches were open. The submariners were working feverishly to repair a mechanical problem between the two hatches. Despite a year-long retrofit, a bolt had come loose on the air vent. The bolt needed to be fixed immediately. After a team meeting, the captain decided to allow both hatches to remain open while the workers tried to fix the problem. Far from being reckless, the decision to keep both hatches open came only after a mechanical error required an urgent solution.

But that wasn’t the end of our investigation.

Next, the CBC News team focused its attention on the wiring where the fire erupted. The fire began after salt water seeped into a set of high-voltage wiring connectors. But how did the water get through the insulation? Surely, the wiring in a submarine would be built to withstand contact with water. That’s when our investigation revealed the wiring where the fire erupted in the Chicoutimi was substandard.

As it turns out, the Chicoutimi’s wiring wasn’t ever brought up to the standards that were established when this class of submarine was first built. The wiring and connectors on its two sister boats were upgraded to include two backup layers of waterproof insulation intended to stop water from coming into contact with the high voltage cables. Our investigation revealed the Chicoutimi sailed without those upgrades. We also revealed the Canadian Navy had no idea its submariners set sail that day with substandard wiring, and failed to learn about the wiring problems until after the fire erupted that injured several of its submariners and killed Lt. Chris Saunders.

For more information on the CBC’s coverage of the Chicoutimi disaster, please see: http://www.cbc.ca/news/background/cdnsubs/newsarchive.html