With men, supplies, and ships obviously concentrating at Pusan and in Japanese ports for a major amphibious operation and the press in Japan referring to the upcoming landings as "Operation Common Knowledge," the UN command feared that it would fail to achieve surprise in the Inchon landings. Exacerbating this fear, the leader of a North Korean-Japanese spy ring arrested in Japan in early September 1950 had a copy of the plan for Operation Chromite, and the UN forces did not know whether he had managed to transmit the plan to North Korea before his arrest. US Navy patrol aircraft, surface warships, and submarines operated in the Sea of Japan (East Sea) and the Yellow Sea to detect any reaction by North Korean, Soviet, or People's Republic of China military forces, and on 4 September 1950 F4U Corsair fighters of Fighter Squadron 53 (VF-53) operating from the aircraft carrier shot down a Soviet Air Force A-20 Havoc bomber after it opened fire on them over the Yellow Sea as it flew toward the UN naval task force there.