The radio station on Oahu, KGMB, usually shut down at night, but when aircraft were making an overnight flight from the mainland the Army Air Force paid for the station to stay on the air. By this means the incoming pilots were given a radio beacon to aid navigation. The arrangement was common knowledge, and when, on the morning of 7 December, Lieutenant Kermit Tyler (Tyler, Kermit) was required to deal with a telephone call from Private Joseph Lockard (Lockard, Joseph) about a blip on his radar, he remembered that the station had been playing all night and that some B-17s were due. He therefore told Lockard not to worry, missing one of the warnings of the attack on Pearl Harbor. The broadcast was also heard by the Japanese. Lieutenant Heijiro Abe, 1st Division, 3rd Attack Unit from Soryu was reassured to hear ordinary music over the air, confirming that the Americans had no thought of attack. At about 0715 KGMB gave the weather forecast, gratefully overheard by the leader of the First Attack Wave, Commander Mitsuo Fuchida (Fuchida, Mitsuo) who had been worrying about conditions over his target. Shortly after 0804 the station sent out a message recalling all military personnel to duty, interrupting a concert to do so, and the call was repeated at 0805 and 0830. Police and firemen were called at 0832 and at 0840 the radio reported an attack by planes with the Rising Sun symbol on their wings. At 1145 Army G-2 (Intelligence) ordered KGMB and the other station KGU off the air as their transmissions were a guide to the enemy.
You can find out more about KGMB in the following Osprey book: