Whichever way you look at it, the definitive version of this SF novel is the 1959 Dobson version. For completeness, there is also an abridged version available on Pilot Books (1964) that was intended for use in schools. Nobody let us read such enjoyable books as this at our school, even though the time period was spot on for it.
This time there is no doubt that we are reading an SF novel. Scout Pilot John Leeming heads for enemy territory in a new, supercharged scout ship to measure the depth of the enemy's hinterland. This is the story of his trip, his capture and his escape using only his brains. And this is where the book scores. It's funny, irreverent, satirical, fast paced but ultimately has a serious intelligent message. None of the "Hitch Hiker" flippancy here. The writing is skilled and as always EFR handles dialogue brilliantly well.
There is even a simple attempt to introduce some alien language, comical in that it sounds like human speech but makes no sense. However, we can understand it as it is always placed in context and the context makes everything clear without resorting to clumsy explanation.
Another one little seen these days, although reprints do appear from time to time. Try to read the complete 1959 version if you can.
