A China Coast Guard helicopter entered Japan’s territorial airspace around the Japanese-controlled, Chinese-claimed Senkaku Islands in the East China Sea on Saturday — just the fourth such incursion by a Chinese aircraft since the end of World War II.

The Defense Ministry in Tokyo said that the Air Self-Defense Force had scrambled fighter jets after a China Coast Guard ship entered Japan’s territorial waters around the islands and launched the chopper, which remained in Japanese airspace for about 15 minutes from 12:21 to 12:36 p.m. The ASDF fighter jets did not fire their weapons or deploy flares.

The airspace violation was believed to be the first by a China Coast Guard helicopter.