"The Ministry of Ungentlemanly Warfare: Churchill's Mavericks" by Giles Milton describes a lot of the equipment that SOE developed - e.g. the original limpet mine depending on condoms and boiled sweets and, of course, developed in someone's shed and tested at the local swimming pool.
Chapter after chapter devoted to figuring out what the Germans were up to on the technology front, then one-upping them. Lots of engineering porn.