Question: During the Battle of Midway, what indicated that an air strike was in route?
About the article "Battle of Midway", section "Initial air attacks".

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Naval Air Station Midway, also known as NAS Midway, Naval Air Facility Midway, and NAF Midway, was a U.S.
Naval Air Station in the Midway Atoll, the northernmost group of the Hawaiian archipelago.
It was in operation from 1941-1993, and played an important role in trans-Pacific aviation during those years.
Through its lifetime, the facility was variously designated as a Naval Air Station, a Naval Air Facility, and a naval base.
It was finally closed on 1 October 1993.
Midway Atoll consists of two small islets, Sand Island and Eastern Island, surrounded by a coral reef.
Most of each islet is taken up by airfields.
The islands were discovered in 1859, and placed under Navy control by President Theodore Roosevelt in 1903.
They gained importance in the mid-1930s as a seaplane stop for the Pan American Airways Clipper planes.
A Navy presence then began building up, and Naval Air Station, Midway Islands was established on Eastern Island in August, 1941.
On 7 December of that year, the base was bombarded by Japanese surface ships as part of the attack on Pearl Harbor.
This was followed by a major buildup of U.S. Navy, Marine, and Army Air Corps squadrons, meant to detect and defeat units of the Japanese fleet.
In late 1942, the Japanese attempted to invade the islands and destroy the nearby U.S. carrier task forces.
From 4-6 December, the Battle of Midway resulted in damage to most of the base, but Navy carrier aircraft sank four Japanese aircraft carriers and one cruiser.
This became the turning point of the war in the Pacific.
After the Battle of Midway, a second airfield was developed, this one on Sand Island.
It became an important stopover for planes heading to the war zone.
It was the origin of a long-range strike on Wake Island by PB2Y "Cornados", and was also used for the submarine war patrols that devastated Japanese shipping.
Activity diminished after the war, and Eastern Island was abandoned in 1945.
The base was placed in caretaker status, and the Naval Air Station was disestablished on 1 August 1950.
It rose again in July 1958 as a base for radar early warning patrols by Navy EC-121 "Warning Star" aircraft.
During the mid-1960s Midway became an important stop for transports moving to and from Vietnam, and the base was redesignated as a Naval Air Station.
In 1970, Eastern Island was once again vacated, this time being designated as a wildlife sanctuary.
After the Vietnam War, NAS Midway mainly served as a refueling stop and a base for occasional Navy patrol planes.
In October 1978 it was downgraded to Naval Air Facility status and dependents were sent home.
With the end of the Cold War, operations dwindled even more.
NAF Midway was disestablished on 1 October 1993.  
The 1st Air Fleet dispatched the Fifth Carrier Division in the Coral Sea during the return from the Indian Ocean.
On May 7 the USN sighted the Port Moresby invasion force and mistook it for the main carrier force.
Admiral Fletcher sent an aircraft strike which sank the IJN light carrier "Shōhō".
After this loss of air cover, the Port Moresby invasion force abandoned its mission and retreated north.
On the same day the IJN sighted and sank USN destroyer "Sims" and oiler "Neosho".
The primary action took place on 8 May.
Both carrier forces sighted and attacked each other.
As a result, "Lexington" was sunk and "Yorktown" was damaged by a Japanese air strike.
USN aircraft managed to damage "Shōkaku", meaning that she and her sister ship were unable to participate in the following operation.
The remaining fleet returned to Japan to prepare for the Midway invasion (Operation MI). 
On 20 June, during the Libyan civil war, NATO strikes in Sorman against what appeared to be civilian homes in a compound belonging to one of Muammar Gaddafi's associates, Khaled K. El-Hamedi, reportedly killed several civilians, including two children and their mother.
NATO admitted carrying out an air strike on a military target in Sorman but deined civilian deaths.
NATO issued a statement that said a precision air strike was launched against a "high-level" command and control "node" in the Sorman area.
On 14 August, the National Liberation Army said it had captured the city in battle during the major coastal offensive.
10 rebel fighters were killed and at least 40 pro-Gaddafi fighters were captured during the battle for the town. 
Battle of Midway.
Midway raid.
Concerned by the US carrier strikes in the Doolittle, Marshall Islands, and Lae-Salamaua raids, Yamamoto determined to force the US Navy into a showdown to eliminate the American carrier threat.
Yamamoto decided to invade and occupy Midway Island, which he was sure would draw out the American carrier forces to battle.
The Midway invasion was codenamed by the Japanese as Operation "MI".
In support of "MI", on 27 May 1942, "Kaga" departed the Inland Sea with the Combined Fleet on her final mission, in the company of carriers "Akagi", , and which constituted the First and Second Carrier Divisions.
Her aircraft complement was 27 Zeros, 20 D3As, and 27 B5Ns.
With the fleet positioned northwest of Midway Island at dawn on 4 June 1942, "Kaga" contributed eighteen D3As, commanded by Lieutenant Shōichi Ogawa, escorted by nine Zeros to the strike against the island.
The carrier's B5Ns were armed with torpedoes and kept ready in case enemy ships were discovered during the Midway raid.
One each of the D3As and Zeros was shot down by AA fire over Midway, and another four D3As were damaged.
"Kaga"s Zero pilots claimed to have shot down 12 US aircraft over Midway Island.
One "Kaga" B5N was launched to augment the fleet's reconnaissance of the surrounding ocean.
The carrier also put up two Zeros on CAP.
Another five Zeros reinforced her CAP at 07:00 and the seven fighters helped to defend the Kido Butai from the first US air attackers from Midway Island at 07:10.
Unknown to the Japanese, the US Navy had divined the Japanese "MI" plan from signals intelligence and had prepared an ambush using its three available carriers, positioned northeast of Midway.
At 07:15 Admiral Nagumo ordered the B5Ns still on "Kaga" and "Akagi" rearmed with bombs for another attack on Midway itself.
This process was limited by the number of ordnance carts used to handle the bombs and torpedoes and the limited number of ordnance elevators.
Thus, the torpedoes could not be struck below until after all the bombs were moved up from their magazine, assembled and mounted on the aircraft.
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 warm up and launch the strike group.
Around 07:40 Nagumo reversed his order when he received a message that American carriers had been spotted.
At 07:30 "Kaga" recovered three of her CAP. 
Admiral Isoroku Yamamoto planned to lure and destroy USN carriers by attacking the Midway Islands in June 1942.
The Japanese were unaware that the United States had broken their naval code.
As a result of this, USN carriers were already in the area when the Japanese attacked Midway.
On 3 June US land-based bombers from Midway attacked the Japanese fleet but scored no hits.
On 4 June, due to the poor reconnaissance efforts and tactical mistakes of Vice Admiral Chuichi Nagumo, USN dive bombers were able to surprise the Japanese carrier force and destroyed three carriers ("Akagi", "Kaga" and "Sōryū").
At the time of the attack the Japanese carriers were in the process of preparing to launch an air strike against the US carriers and their hangars were full of loaded aircraft, bombs and aviation fuel which decisively contributed to their destruction.
Carrier "Hiryū" managed to survive the attack and Rear Admiral Tamon Yamaguchi launched a strike against "Yorktown".
Aircraft from "Hiryū" managed to cripple "Yorktown", which was later sunk by a Japanese submarine I-168.
In response, US launched a strike against "Hiryū" and sunk her.
That day the Japanese lost four aircraft carriers and much of their experienced aircrew.