By 1918 Japan had decided to build a new fleet of eight battleships and eight battlecruisers over the next fifteen years. Of this "8-8 Plan", the last four (#s 13-16) would be the largest warships Japan had ever built and similar to the "Saints"-class of giant British battlecruisers being laid down. Japan was miffed when the terms of the 1926 Washington Naval Treaty forbade any further building and limited Japan to the six "middleweight" Nagato/Akagi/Tosa classes, even forcing two of these to be converted into aircraft carriers. Design studies continued in secret, modernizing various features to keep up with trends. The envisioned new 18.1" guns were tested as "land fortification" guns. After seven years of the Treaty the Japanese Navy grew impatient and, in secret, began constructing a huge hull behind tall sisal mats in a special building basin. Foreigners were prohibited and suspicions arose, but nothing could be verified. The launching was done in darkness at great risk. Builder's trials were also done during the long nights of winter, but by summer of 1936 Kii was ready.

In 1937 the 10-year Treaty came up for renewal and all the signatories except Britain were chafing at the bit to increase gun caliber or tonnage limits. Sixteen-inchers and 35,000 tons, respectively, were just "too small" for a real battleship. Britain alone could afford to be both smug and 'concerned' as she possessed the world's three largest warships with the world's largest guns, built just before the Treaty took effect: the two 18"-gunned St. Andrew and St. Patrick, and the 20"-gunned behemoth Superb. The extreme speed, range, and gunpower of Superb made a nice showpiece, but they were attained by a ridiculous sacrifice in protection. The "Saints", on the other hand, were well-balanced, formidable warships without equal in the world. That was about to change.

Japan was about to announce her official disinterest in renewing the Treaty when an off-course American flying boat accidentally overflew Kii on a rare daytime trials run. An astute naval attaché aboard the plane took clear, unmistakable photos. The naval world was shocked at Japan's deliberate subterfuge, and was abuzz with plans for recrimination. Instead, the Treaty collapsed into a renewed world-wide construction frenzy to complete any 'puny' 35,000-tonners and get on with new ones to 'match' Japan. Japan herself had no actual plans for a repeat Kii and was stunned by the world reaction to "one little battleship". Japan even promised to start no new battleships and convert two existing ones, Tosa and Owari, to aircraft carriers, but Japan's flagrant breach of the Treaty and large hulls laid down (three CV's of the Shokaku class) couldn't allay the world's fears. To regain a measure of world respect, Japan adhered to her promise by only renovating her existing older battlewagons, but gave up in disgust two years later and began building even bigger warships.

Kii bombarded Chinese cities on her maiden voyage, and later accompanied cruiser Ashigara to Britain's Coronation Naval Review in 1937. Kii became the hot topic of any naval conversation. In the summer of 1940 Russia assisted and allowed the massive Kii to use the Polar Route from Japan to Germany to test the feasibility of transferring future large Soviet warships to the Pacific via the shortest route. Once in Baltic waters, Japan's premier battleship remained idle for more than a year as neither the British nor Soviets would allow Kii to pass their country's controlled waters again. When Japan declared war on the Soviet Union in early 1942, Kii's 18" guns went up against a newly-completed Krasny Tovarishch, also with 18" guns. Russian inexperience and Kii's torpedoes gave her a victory as the heavily damaged K.T. struggled back to Leningrad to sit out the war.

Breaking out into the North Atlantic with the Tirpitz, Kii headed south, rounded the Cape of Good Hope, then headed east to rendezvous with a Japanese Striking Force steaming west from the Seychelles. Out of range of either Japanese or Allied aircraft, the Greek battleship Salamis engaged Kii but was clearly outmatched and sank before any Allied help could arrive. The delaying action enabled Hawker Henley carrier dive bombers from HMS Excalibur to swarm over the lone Kii and put her out of commission before Japanese interceptors could intervene. When the main Japanese fleet was turned back, Allied carrier bombers returned to the wallowing Kii and finished her off at leisure.