The Imperial Japanese Navy (IJN) was the navy of the Japanese Empire.[1] In the first half of the 20th century, it was one of the largest and most advanced navies in the world. However, the Pacific War ensured the demise of the IJN and dissolution of Japan's empire. 

The Russo-Jap War and World War One

In the early 20th century, Japan's navy was influential in the Russo-Japanese War of 1904 – 1905. It had expanded in the decade before with more than 100 additional warships added to the IJN including battleships, cruisers and destroyers. With a fleet of more modern battleships Japan defeated the Russian navy at the Battle of Tsushima. This triumph ensured a more general victory for Japan in that war.

The IJN provided naval support for the Triple Entente during the First World War. At the Battle of Tsingtao Japan launched the first sea-launched airstrikes targeting German positions on land. During the war, Japan defeated a number of German colonies in the East and absorbed them into the Japanese Empire.

The IJN's Expansion During the Interwar Period

During the interwar period, the navy constructed a new aircraft carrier fleet. Japan added the first carriers to its fleets in the early 1920s, and gradually constructed a fleet of 10 large aircraft carriers.  These were supported by carrier aircraft such as the A6M Zero and other dive and torpedo-bombers.

The first IJN carrier built was the Hōshō. This was the first purpose-built aircraft carrier added to any navy. That remained a part of Japan's navy up to the Pacific War.

In addition to this, the navy laid the first blueprints for the Yamato-class battleships. The Yamato-class battleships were constructed in the 1930s, and by the early 1940s the IJN added them to its fleets. They were the two largest battleships built by any navy, the Yamato and the Musashi, both of which were about 72,000 – 73,000 tons.

Other exciting additions to the IJN were not warships, but torpedoes. The Long Lance torpedo was a long-distance torpedo for destroyers. This was the most advanced torpedo in the world during the early 1940s.

The Pacific War Begins

The Western economic embargo of the early 1940s left Japan with little oil. The Japanese were at war with China during the 1930s, and this required more extensive fuel supplies. With oil running out, Japan targeted European colonies in the region and Pearl Harbor where the U.S. Pacific Fleet was stationed.

To defeat the U.S. Pacific Fleet, Japan sent a fleet of six aircraft carriers to Pearl Harbor. When they arrived, the navy launched hundreds of planes toward the harbor where they bombed the U.S aircraft and battleships in port. The United States lost hundreds of aircraft during the raid, and battleships at Battleship Row were also destroyed. Although the U.S. carriers were not at Pearl Harbor. 

Pearl HarborCredit: This is a public domain image from Wiki Commons.  
The above image is licensed under public domain on Wiki Commons.  

In the months that followed, the IJN was effective in its battles with the Allied navies, most notably at the Java Sea. On the 26th, the Allies detected a Japanese invasion fleet heading for Java. As such, a fleet of ABDA (American, British, Dutch and Australian) warships left their ports in Surabaya to search for Japan's Java invasion fleet. The fleet included more outdated cruisers and destroyers, but was comparable in size to the Japanese fleet that was soon intercepted.

The Battle of Java Sea

On February 27, the Allies located and intercepted Japan's fleet in the Java Sea. The Japanese fleet fired a barrage of their long-range Long Lance torpedoes that sank one destroyer. The HMS Exeter was also hit by a shell, which wiped out most of the ship's boilers. The damaged boiler rooms reduced the Exeter's speed, and it began to withdraw from the battle behind an Allied smoke screen.

The HMS Electra covered the Exeter as it retreated the battle. IJN destroyer and cruiser fire knocked out the Electra's gun mounts and damaged its boiler rooms, and as fires spread and the warship listed to port its crew abandoned ship.  Further Japanese torpedo firing split the Kortenaer, which sank soon after.

Hereafter, the fleets lost contact for a few hours. After dark four U.S. destroyers, which were short on fuel, withdrew from the battle and further depleted the ABDA fleet. Another Allied destroyer was lost at sea, probably because of an uncharted mine. Later in the evening the IJN and ABDA fleets resumed the battle, and Japanese warships sank two further Allied cruisers. Hereafter, the remaining ABDA fleet began to withdraw from the battle.

On the 28th, the retreating Allied warships sailed into the Sundu Strait. Here they ran into a Japanese landing force escorted by nine destroyers. The Houston and Perth charged toward the transport ships, but IJN escort fleet warships quickly closed in on them before they could have any impact on the landings. The IJN fired a barrage of torpedoes that sank Allied cruisers at the Sundu Strait.

On March 1, the Exeter, escorted by two further Allied warships, set sail for Colombo. However, IJN cruisers and destroyers intercepted them in the Java Sea, which finished off two of the remaining Allied ships. The USS Pope briefly lost the enemy warships before Japanese aircraft rediscovered it and sank it from the air.

The Battle of Java Sea effectively ended here. The Japanese had sunk nearly all the ABDA fleet, except four U.S. destroyers that made their way back to Australia. As such, after the battle Japanese troops soon flooded into Java and defeated the Allied armies stationed there in the month of May. The Japanese Empire absorbed the East Indies until the end of the Pacific War.

The Battle of Coral Sea in 1942 was the first naval battle between carrier fleets. It was there that the IJN took on U.S. Navy carriers and sank the Lexington. However, the USA still held Port Moresby, which was one of the primary objectives of Japan's operation.

The IJN's Defeat

At Midway the Japanese navy lost four aircraft carriers. The original plan was to occupy the Midway Atoll and defeat the U.S. aircraft carriers sent to defend it. But the Allies had decoded the JN-25 code that provided them with details of the Japanese battle plan, and with a fleet of three U.S. carriers dive-bombers took out the IJN aircraft carriers around Midway.

Thereafter, there were further naval battles during the Eastern Solomon Islands Campaign.  The Battle of Eastern Solomons was one in which the IJN lost one light carrier and destroyer. The Japanese navy sank the Hornet aircraft carrier at the Battle of Santa Cruz. However, the overall losses the IJN had during the full campaign considerably depleted its logistical backbone.

The Midway defeat greatly reduced the navy's fleet air arm. In later battles during 1944, at the Battle of Philippine Sea and Leyte Gulf, the Japanese navy lost all its remaining aircraft carriers and most of its surface warships. The Battle of the Philippine Sea was the IJN's attempt to beat off Task Force 58 and the U.S. invasion of the Marianas. The plan was for land-based aircraft in the Marinas to provide more support for the carrier fleet planes. However, the Allies destroyed a substantial number of planes on the ground with airstrikes; and in the battle that followed sank three IJN fleet carriers and the majority of their aircraft.

The Battle of Leyte Gulf was the coupé de grace for the IJN. As Marines invaded Leyte, Japan's navy devised a bold plan to defeat the Allied operation in the Philippines. It included a decoy carrier fleet intended to lure away the Third Fleet further northwards so the Center Force, which included the world's largest battleships, could strike at the invasion fleet around Leyte. Although the Third Fleet took the bait, the Center Force could still not do enough during the Battle off Samar to defeat the Allied campaign. After taking some losses, it withdrew from the battle. 

The few IJN warships that remained intact after that battle became the target for regular Allied airstrikes at their naval bases in Japan and elsewhere in the Pacific. The U.S. Navy defeated the Yamato during Operation Ten-Go, when U.S. aircraft bombed the ship out the water.

As such, by the end of the war little remained of the IJN; and those warships that did remain did not have enough fuel. The Allies defeated the Japanese Empire in 1945. In the postwar period, the IJN was disbanded in 1947.