She was the lead ship of her class, built under the 1930 London Naval Treaty, which imposed limits on cruiser, destroyer, and submarine tonnage for the United States, Great Britain, and Japan. Four ships were built in the class, with Mogami slipping down the ways on March 14, 1934, at Kure Navy Yard. Mogami would go on to a lengthy but luckless career in the Imperial Japanese Navy.
The Mogami, like her sisters, displaced 13,440 tons, could crack the waves at 35 knots, and packed 10 8-inch guns and 12 Long Lance torpedoes. With her bulky superstructure, she vaguely resembled a battleship and was a formidable weapon of war.
She was also a popular assignment for her 850-man crew. Mogami and her sisters were air conditioned and had steel tube bunks in place of hammocks for the seamen, cold water drinking fountains dispersed throughout the ship, and more extensive refrigeration spaces for food, which meant better chow. Like all Japanese ships, Mogami had several pickle lockers in different parts of the ship, for careful study had found that a crew that ate pickles daily was more efficient than one that did not. The air conditioners proved noisy and were not installed on future ship classes.
All four ships of the class—Mogami, Mikuma, Kumano, and Suzuya—were assigned together as Cruiser Division 7 (CruDiv 7). Bad luck began right away. In late 1935, Mogami suffered typhoon damage, her bow crumpled in her first deployment due to poor welding. The crew found the hull had warped so badly they could not train her turrets. An investigative board ordered the ship disarmed and drydocked for massive reconstruction.
