In April, Hiryū's aircraft helped sink two British heavy cruisers and several merchant ships during the Indian Ocean Raid.

The loss of Hiryū and three other IJN carriers at Midway was a crucial strategic defeat for Japan and contributed significantly to the Allies' ultimate victory in the Pacific.

The ship's power and slim, cruiser-type hull with a length-to-beam ratio of 10:1 gave her a speed of 34.3 knots (63.5 km/h; 39.5 mph)[6] and made her the fastest carrier in the world at the time of her commissioning.

The boiler uptakes were trunked to the ship's starboard side amidships and exhausted just below flight deck level through two funnels curved downward.

The flight deck was only 12.8 meters (42 ft) above the waterline and the ship's designers kept this figure low by reducing the height of the hangars.

[8] This caused problems in handling aircraft because the wings of a Nakajima B5N "Kate" torpedo bomber could neither be spread nor folded in the upper hangar.

According to historian Mark Stille, the weapon had many faults including an inability to "handle high-speed targets because it could not be trained or elevated fast enough by either hand or power, its sights were inadequate for high-speed targets, it possessed excessive vibration and muzzle blast, and its magazines were too small to maintain high rates of fire".

[19] Two months later, the 2nd Carrier Division, commanded by Rear Admiral Tamon Yamaguchi, was assigned to the First Air Fleet, or Kido Butai, on 10 April.

From a position 230 nmi (430 km; 260 mi) north of Oahu, Hiryū and the other five carriers launched two waves of aircraft on the morning of 7 December 1941 Hawaiian time.

That ship, the battleship Pennsylvania, was in drydock and its position was occupied by the light cruiser Helena and the minelayer Oglala; all four torpedoes missed.

[32] Hiryū and the other carriers arrived at Staring Bay on Celebes Island on 21 February to resupply and rest before departing four days later to support the invasion of Java.

The four carriers launched an airstrike of 180 aircraft against Tjilatjep on 5 March and set the town on fire, sinking five small ships, and damaging nine others that later had to be scuttled.

[33] Two days later, they attacked Christmas Island and Hiryū's aircraft sank the Dutch freighter Poelau Bras before returning to Staring Bay on 11 March[20] to resupply and train for the impending Indian Ocean raid.

This raid was intended to secure newly conquered Burma, Malaya, and the Dutch East Indies against any Allied attack by destroying base facilities and forces in the eastern Indian Ocean.

[34] On 26 March, the five carriers of the First Air Fleet departed from Staring Bay; they were spotted by a Catalina about 350 nautical miles (650 km; 400 mi) southeast of Ceylon on the morning of 4 April.

Hiryū contributed 18 B5Ns and 9 Zeros to the force; the latter encountered a flight of 6 Fairey Swordfish torpedo bombers from 788 Naval Air Squadron en route and shot them all down without loss.

The British were attempting to find Nagumo's ships all morning and Hiryū's Zeros on CAP over the fleet helped to shoot down an RAF Catalina, shot down a Fairey Albacore torpedo bomber and drove off another from the carrier Indomitable.

While this was going on, Akagi narrowly escaped damage when 9 British Bristol Blenheim bombers from Ceylon penetrated the CAP and dropped their bombs from 11,000 feet (3,400 m).

After launching the dive bombers that sank Hermes and the other ships, the First Air Fleet reversed course and headed southeast for the Malacca Strait and Japan.

[36] On 19 April, while transiting the Bashi Straits between Taiwan and Luzon en route to Japan, Hiryū, Sōryū, and Akagi were sent in pursuit of the American carriers Hornet and Enterprise, which had launched the Doolittle Raid against Tokyo.

[41] With the fleet positioned 250 nmi (460 km; 290 mi) northwest of Midway at dawn (04:45 local time) on 4 June 1942, Hiryū's portion of the 108-plane airstrike was an attack on the facilities on Sand Island with 18 torpedo bombers, one of which aborted with mechanical problems, escorted by nine Zeros.

[43] At this time, Nagumo's carriers were attacked by six U.S. Navy Grumman TBF Avengers and four USAAC Martin B-26 Marauders, all carrying torpedoes.

This process normally took about an hour and a half; more time would be required to bring the aircraft up to the flight deck, and to warm up and launch the strike group.

The high altitude of the B-17s gave the Japanese captains enough time to anticipate where the bombs would land, and they successfully maneuvered out of the impact area.

[48] These fresh Zeros helped defeat the next American air strike from Midway, 11 Vought SB2U Vindicator dive bombers from VMSB-241, which attacked the battleship Haruna starting around 08:30.

They attempted a torpedo attack on Soryū, but all of the American planes were shot down by the 18 CAP fighters, leaving one surviving aviator treading water.

Four more B5Ns fell during the attack, but two of the survivors managed to score hits on Yorktown that damaged three boilers and knocked out all electrical power so that she could not pump fuel oil to starboard to counteract her six-degree list to port.

At 16:45, Enterprise's dive bombers spotted the Japanese carrier and began to maneuver for good attacking position while reducing altitude.

At 16:56, just as the first Dauntlesses were beginning their dives, Nagumo ordered a change in course to 120 degrees, possibly to prepare to recover his reconnaissance floatplanes, that threw off the aim of the leading SBDs.

Beginning at 17:42, two groups of B-17s attempted to attack the Japanese ships without success, although one bomber strafed Hiryū's flight deck, killing several anti-aircraft gunners.