Another excellent edition to Butlers secret projects series. Some minor quibbles: it is never made clear on the title pages inside the book what exactly is the aircraft depicted on the excellent front cover of the book (I assume it is the tailless maritime patrol bomber listed later) and referring to the lockeed hudson as being developed from the twin electric aircraft (Electra?) and other minor typos.
Most of the information, if not all, has been available for years from the Putnam range for one, l suppose they where secret back in the time but
a lot in the book became mainstream! Best bit is the Dust Cover illustration