We need to translate visible text to Japanese, preserving HTML tags exactly. Only output translation, nothing else. We must translate all visible text content, including alt text? There's no alt. Also translate link text (the visible part). The link URLs remain unchanged. Let's go through HTML:

The Manhattan Project was one of the best-kept secrets...

Translate that sentence. Second paragraph with strong em: "Workers had no idea..." etc. Need to translate that whole content, preserving tags ... .

The Manhattan Project

=> translate heading text.

The Manhattan Project was a research and development project during the Second World War...

translate.

The Project saw its fruition in 1938 when German scientists Otto Hahn and Fritz Strassman discovered nuclear fission. The discovery of these German scientists led Albert Einstein and Leo Szilard to warn then President Roosevelt that the Germans may be building an atomic bomb.

translate.

It was officially created in 1942 and was named Manhattan Project because it was first located at 270 Broadway, Manhattan.

translate.

The Project gave way to new warfare – the atomic