The 1930s and early 1940s had seen Japan place great stress on its heavy cruiser force. During the early part of this period, her heavy cruisers had set something of a world standard but this position had been lost as American cruiser design advanced. The Mogami class cruisers had been a significant design failure and had required repeated rebuilds before they could be considered satisfactory. The next class, the two ships of the Tone class were one of Japan's more eccentric designs, armed with eight 8 inch guns in four twin turrets forward while the rear was cleared for aircraft operations. This was also unsatisfactory and the next pair of heavy cruisers, the two Ibuki class ships were essentially Mogami class cruisers with the faults corrected.
By the time the Ibukis were entering service, the first four Japanese heavies, the four Furataka class cruisers, were approaching replacement. They were the smallest of the type in Japanese service, armed with only six eight inch guns each and were painfully obsolete in both design and capability. The next class of heavy cruisers were intended to be their replacements. It was also intended that the new class would return Japan to its leading position as a heavy cruiser design center.
The new class of cruisers were an enlarged version of the Ibuki class, the hull lengthened to include an extra eight inch twin turret aft for a total of twelve guns in six twin mounts. However, a dispute arose at this point; the Americans had decided that the greater rate of fire from six inch guns was more valuable than the increased shell weight of eight inchers. Since the Japanese 6.1 inch L60 was a much superior weapon to the American 6 inch L47 (or so the Japanese thought), would it not make sense to follow suite? The new Asama class could carry 18 of the 6..1 inch guns, giving them a 50 percent superiority over the latest American cruisers. This would also have the merit of standardizing Japanese gunnery further by using the same gun on their heavy and light cruisers. The debate raged backwards and forwards, leading one designer to suggest equipping the ship with three triple 6.1 inch mounts forward and three twin eight inch mounts aft. To his incredulous horror, the suggestion was taken seriously and was almost put forward as a viable design option.
At this point, a new ingredient was thrown into the mix. Japanese ordnance designers had produced a new mount for the 6.1 inch L60 that offered full dual-purpose capability. The twin mount had a full 70 degree elevation and a sustained rate of fire of 15 rounds per barrel per minute. Elevation and train rates were fully compatible with anti-aircraft use. This new mount offered both effective anti-surface capability and good anti-aircraft firepower. Although the 8 inch proponents put up a desperate rearguard action, the decision was taken; the new cruiser would have 12 6.1inch L60 guns in six twin turrets.
As soon as this argument was resolved, a new issue was raised. Older Japanese heavy cruisers had a virtually standard anti-aircraft battery of four twin 5 inch mounts, two each side. The Asama class had replaced these with the 3.9 inch L65 but the number still remained four on each beam and this was obviously no longer adequate. The designers worked in an extra 3.9 inch twin on each beam by deleting one of the two banks of torpedo tubes, then added another by eliminating the aircraft handling facilities. Traditionalists exploded at this elimination of traditional Japanese cruiser features but half way through the battle over the design, news of the sinking of the USS Shiloh was received. In Japanese naval circles, this outweighed even the destruction of Germany. If the Americans couldn't stop and air attack with their immense fleet, what chance did Japan stand? Obviously a massive increase in anti-aircraft firepower was needed and the Asama class offered just that.
The first Asama class cruiser was laid down in 1948 and entered service in 1953. Her sisters followed at yearly intervals, one being commissioned in each of 1954, 1955 and 1956. Unlike earlier Japanese heavy cruisers, the Asama class were instantly successful ships. Under normal circumstances, these large and powerful cruisers would probably have been rebuilt as missile ships but events conspired against them receiving any major rebuild and they only got minor upgrades over the years. The Asama herself was sunk during the Pescadores Incident but the other three remained in service until the middle 1990s.
The Asama class also had an unusual distinction in that they were the first Japanese designed ships in some years to be exported. In 1956, the Chilean Navy decided that it needed to modernize and revitalize its fleet. It therefore decided to order two new heavy cruisers to replace its ancient battleships and eventually settled n the Asama class. Two ships of a slightly modified design were ordered as the Almirante Latorre and the Almirante Cochrane. They were both laid down in 1957 and delivered in 1961. At time of writing, these two ships remain in service. An unusual note is that a further Chilean naval rearmament saw the country purchase four Wellington class destroyers from Australia and these six ships frequently formed a single operating unit. During the Anglo-Argentine Falklands War of 1982, the squadron was deployed south in the event of the fighting spilling over into Chilean territory (and, it is tacitly admitted, as a demonstration of support for the UK).
The Asama class were to have been followed by a repeat class incorporating some minor revisions, primarily the reconfiguration of the stern to provide a helicopter deck and a new mainmast to carry additional radar equipment. These Modified Asama class cruisers would have been the replacements for the old Nachi class ships but the proposal fell foul of the Japanese Navy's Strategic Review and the ships were cancelled before being laid down.