This paper shows the actural circumstances of Japanese naval radar and their wartime urgent measures for radar. At the end of war Japanese naval radar was widely spread over. : about 250 land-based radar sites, 100 million yen costs, 30 radar types, 500 radar officers and 10 thousand radar operators. For the purpose of that, Japanese navies took the counter plan from the half time of the war. The main urgent measures of this are as follows. THe first, many young naval officers graduated from university got into the naval radar school which named Fujisawa Kaigun Densoku Gakkou (Naval Radar School) established on September 1944 at Kanagawa Prefecture. The second, the new naval manufacture for radar named Numazu Kaigun Khosho (Navy Yard) established on June 1943 at Shizuoka Prefecture. The third, the radar was designed simply for the purpose of easy carriage, reasonable cost and long time operation. The typical radar was the Mark 1 Model 3 radar which was operating at 150 MHZ, peak power 10 KW. So many radar sites were constructed at pacific coasts of Japan, but there was no radar war with United States because of the Japanese primitive radar.
Soon after the dropping of the Hiroshima bomb, Yoshio Nishina, an experimental physicist who was in charge of the Army's development of nuclear weapons at Riken, the Institute of Physical and Chemical Research, could understand that it was an atomic bomb because its energy release given in Truman's statement coincided with the one that his colleague Hidehiko Tamaki estimated a few years ago. This suggests that they knew of the magnitude of nuclear explosions. Uraniumu bakudan (uranium bomb), Japanese physicists' bomb at the time, is, however, known to be a kind of nuclear reactor out of control. The "bomb" of this kind is not very powerful because it is based on a slow-neutron reaction. This paper challenges to reproduce Japanese physicists' calculations at the time, and shows that they thought that they could explode their uraniumu bakudan, a slow- reactor bomb, with a quite high efficiency. This led them to expect that the energy release from their bomb would be of 20 K ton TNT equivalence that accidentally coincided with the energy release of the Hiroshima bomb.
In this paper, the author investigated how S.Shinjyo established his conception of the nature of our Galaxy and of spiral nebulae. S.Shinjyo founded the Institute of Cosmical Physics at Kyoto Imperial University, the second laboratory of astronomy in Japan. From 1915 to 1927, he studied the theoretical stellar evolution and established the eccentric nucleus theory that explained how the Cepheid Variables changed their brightness. In his papers, he mentioned not only stellar evolution but also the nature of our Galaxy and of spiral nebulae. Many astronomers were doing similar work at this time. The author focuses our attention to 18 papers by S.Shinjyo. It is important not only to investigate his papers so as to track the establishment of his conception but also to look at other contemporary Japanese papers on conception of the nature of our Galaxy and spiral nebulae. In his 1915 paper, he wrote that our Galaxy has a diameter of 6,600 light years and a spiral structure, and that spiral nebulae is anoter Galaxy. The 1916 paper proposed that our Galaxy didn't have a spiral structure but an ellipse structure. In the 1922 paper, he extended our Galaxy's diameter to 30,000 light years and introduced Shapley's conception of the nature of our Galaxy. In 1925, S.Shinjyo applied Shapley's conception and showed that the spiral nebula is not another Galaxy but rather a large meteoric group. In 1927, S.Shinjyo introduced Hubble's study of M31 explaining that it is 1,000,000 light years away and 45,000 light years in diameter. This means that he agreed the spiral nebula was indeed another Galaxy. Shapley's and Hubble's works influenced S.Shinjyo's work on spiral nebulae. This didn't mean that S.Shinjyo only followed the tendency of international astronomy. He integrated these conceptions, because they were not incompatible with his stellar evolution. But, this literature review generally shows that observational astronomy in Japan depended on the research tendencies of large telescope observational astronomy in America.