Japanese fishing boat contaminated with radioactive fallout during 1954 Castle Bravo hydrogen bomb test

The transcript describes a radioactive incident involving a Japanese fishing boat, the Fortunate Dragon, which was exposed to radioactive ash following an H Bomb explosion. Despite being outside the designated safe area, the boat and its crew were affected by the fallout, unaware of the deadly nature of the ash.

How many crew members were aboard the Fortunate Dragon?

What did the crew of the Fortunate Dragon not know about the falling ash?