In the forenoon on 4 June Nagumo's fleet still had just sketchy ideas on the force that was opposing them. They had still only sighted one U.S. carrier, the U.S.S. Yorktown. Aboard the carrier Sōryū there was two prototype versions of a new plane, the Yokosuka D4Y Type 2 Suisei (Comet) later named ‘Judy’ by the allies. The D4Y was developed as a dive bomber and later replaced the ageing D3A'a (see 4. The attack on Midway - The 'Val') but the first examples turned out to be too unstable for dive bombing. Their long range and fast speed however made them useful as scouting planes therefore these two was now present on Sōryū. One of these were sent off with specific instructions to find and identify the American force.
So Pilot Officer First Class Iida Masatada and Wireless Operator Kondō Isamu climbed into their D4Y and took off heading in the direction of the last known position of the American carrier, the USS Yorktown. To their astonishment they found not one but three American carriers with escorts. They had sighted the TF-16 with U.S.S. Enterprise and U.S.S. Hornet. They tried to radio this back to the Japanese fleet but the message didn't reach through. It later turned out that their radio was out of commission.
With the mission complete they returned to Sōryū only to find it ablaze. Not only that but also the Akagi and the Kaga was on fire. Fortunately they found the carrier Hiryū still intact. However her deck was spotted with Tomonagas torpedo planes (16. Japanese revenge - The 'Kate') so they flew over the deck and dropped a tube with a message describing their sightings. Finally the Japanese knew what they were up against. They then had to circle the carrier until the deck was clear and landed just ahead of Hiryūs dive bombers returning from their attack on USS Yorktown. However some hours later Hiryū was attacked again and this time she did not escape.
Shattered Sword - The untold Story of The Battle of Midway (Book)