この記事では北の漁船じゃなくて warship って言ってるけど・・・
https://www.koreatimes.co.kr/www/nation/2018/12/205_260807.html

"The vessel used fire-control radar not because of the P-1,
which was flying in Japan's air defense identification zone,
but because we tried to trace a North Korean warship drifting
near the inter-Korean sea border," a Navy official told Yonhap
News Agency on condition of anonymity.