Reflecting on the Stainless Steel Rat books and indeed the Stars & Stripes ones, I have a sense now that Harry Harrison was effectively a YA author before that term was in use. If we look at those books they are very much wish fulfillment for teenage boys. While he might not have been explicit about it, he (or his agent) knew his market well and so he wrote effectively for it. If you think of whose bookshelves you would have seen those books on, he was right on target with his demographic, but as we are showing here, less likely to actually appeal to/satisfy a wider audience.