The main character, Thomas Lynch, carries a Colt 1903 pocket pistol with him through most of the novel. He originally bought the weapon as a non-regulation backup for his rifle before he shipped over to France with the British Expeditionary Force in 1939. In the prologue, Lynch uses the pistol to kill several Germans, and it reappears near the end of the book...
And that is the full tally of all the firearms that appear in the novel! It's quite the list, and I don't think I've missed anything. There will be a few new entries for the second book, Operation: Bedlam, so I'll write a follow-up post when that book is published.