They collided shortly after takeoff due to human error while heading to an exercise site. This is what emerges from the outcome of the preliminary investigation conducted by the Maritime Self-Defense Force (MSDF) into the plane crash that occurred in Japan on 20 April 2024. That day two Mitsubishi SH-60K aircraft of the navy collided on the high seas. 

According to the report, as also explained by the Japanese Ministry of Defense, Minoru Kihara, after taking off from a naval vessel sailing the waters of the Pacific Ocean, the pilots of the two helicopters did not fully realize the mutual proximity of the aircraft. At that point the aircraft collided, crashing near the Izu Islands, south of Tokyo, before the start of a night training session. 

To be precise, it was "an anti-submarine warfare scenario" that was set up "suddenly", to be as real as possible. At that point "both ships and helicopters come into action with frenetic activity". Regarding the accident, "we found little evidence that the two aircraft attempted to avoid a collision", reads the report from the Maritime Self-Defense Force.