On 23 October, Kootenay was in the North Atlantic, approximately 210 nautical miles west of Plymouth, as part of a task force of 10 ships and on its voyage home. The ship was sailing with a full complement of 12 officers and 237 seamen.
Early that morning, the Kootenay and HMCS Saguenay broke off from the task force to conduct full-power sea trials, routine tests conducted every quarter. Shortly after 8 a.m., while running at full power, the crew reported hearing a sound like “a rising organ note." Seconds later, a massive explosion rocked the engine room, sending a massive fireball through the ship’s main interior passageway. Within minutes, thick black smoke had spread throughout the ship.
In December, the investigation found that the explosion in the ship’s gearbox was caused by human error — a faulty installation during a refit four years earlier.
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“The explosion is considered to have been caused by the spontaneous ignition of oil and oil vapour through the gross overheating of the high speed pinion bearings," the investigation report concluded. "The cause of the overheating was the incorrect fitting of the insert bearing shells, which resulted in the direct oil supply being completely cut off.”