Dear Siegfried!
Once you click the link to the website, there is another link over to the "Suddhadib (Hardeep) Attack RESEARCH" page that lists a lot of backgrounds of the attack.
But to answer your question here in the forum, here is why a Thai ship was target of British RAF bombers.
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Here a visual recreation of the attack on the S.S. Suddhadib by RAF B-24 Liberator Squadrons 99 and 159 out of India on 1st June 1945. The video is a compilation of 29 individual digital illustrations which I have worked on for many weeks while given accurate attention to historical details...