Though it's aimed at bombering US military base in Japan, ballistic missiles didn't hit nearby sea, but hit Sea of Japan.
Otherwise, they tried to make sure about the travel distance of the missiles?
If so, they should have tried to launch them and make them fly the same distance with or longer than that between North Korea and Okinawa, where US military base is located.
What kind of data did they want to obtain?
It's veiled with mystery.