Why do you think the author said that the book is “least of all an adventure”?

It talks about the cruelty of wars.

Explanation:

The author said that the book is "least of all an adventure" because it talks about the cruelty of wars unlike other books that talks about the heroic experience of soldiers and armies.In this book, the author writes about the dreadfulness of death and war from the eyes of the soldiers. The reference of the statement “death is not an adventure to those who stand face to face with it” in the book reminds us that the experiences of the soldiers were more than just adventure. It was shattering, horrifying and daunting.

It turns into vapor and goes into the atmosphere