DECEMBER 1945

Of the twelve of the Harrisburg class boats completed by mid-1945 three were lost in Japanese waters near the end of the year. The Japanese had developed a high frequency radar in the one and one quarter meter band that could detect a snorkel at ten miles. This may have gone without notice and the losses would have continued had it not been for some very good interpretation of pictures taken of a Japanese bomber. The Japanese were known to have radar but unlike the microwave radar the US and Britain developed which operated in 10 gigacycle bands with waves a couple centimeters long it was in the two meter band at about 140 Megacycles. The submarines had a receiver to scan this band. If a signal got too strong they would dive. The two meter radar couldn’t detect the snorkel unless it was within two miles and the antenna was too big to be carried by aircraft so it was only a threat if there were ships nearby. A picture of a Japanese patrol bomber showed an antenna the photo interpreter didn’t recognize. He noted it and had it reviewed by an electronics expert. The answer came back, this was some kind of radio antenna. The interpreter was a ham operator and had some knowledge of radio. He measured the antenna and included in his report that the Japanese planes might be using a radio on the one and a quarter meter band at about 220 Megacycles. This caused quite a level of concern because the 450 MC radios in the three quarter meter band might not be safe. This was the first indication the Japanese had developed communications above 150 megacycles in the two meter band.

Within a week the B-17SA’s flying over Japan had a new task. Two new radios were installed. They continually scanned the frequencies from 150 to 550 Megacycles. Both had alarms to alert the crew if any signals were detected. If the alarm sounded the crew would record the frequency and listen to the traffic to determine the origin. The first flight out found traffic in the three quarter meter band as expected. It was not any kind of voice transmission, it was pulses, most likely a radar set. The Japanese had made an advance in radio technology to achieve this but had not made the advance to get to the higher frequencies. The 450 MC radios were safe.