Picturegoer wrote: "One of the best spy melodramas yet made. In spite of its stretching of the long arm of coincidence and equally of the imagination it always suceeds in being convincing. ... Eric Portman is excellent as the airman who, in spite of his outward self-assurance, has a yellow streak. Ann Dvorak scores too, as the woman he blackmails into helping him. There are two outstanding character studies in a cast which has not a weak spot. They are given by Beatrice Varley and Martin Miller as two ex-Fascists who are browbeaten by a Nazi agent."
The Monthly Film Bulletin wrote: "An exciting story, well scripted and produced with tremendous attention to detail. The direction is admirable, the pace deftly adjusted and the photography and lighting noticeably good. Eric Portman's characterisation of Kohler is first-rate; he combines the reserve of the Englishman, the cruelty of the German bully and the latter's inherent cowardice quite brilliantly. He is supported by a cast that is of the highest order, especially Martin Miller as Krohn, Walter Fitzgerald as Inspector Milne and, in a small part, David Peel as Michel Berthelot. Ann Dvorak gives a very thoughtful interpretation of the part of Barbara Fenwick, and Barry Jones brings a natural charm to Dr. Fenwick that would have been an enormous comfort to his patients. The whole film is so convincingly made that it is only in retrospect that the constant presence of the long arm of coincidence is realised."
The Daily Film Renter wrote: "Brilliant casting, with star almost out-acted by superlative support. First-rate production. Clear-cut and original job, which holds a fascinating grip on the imagination from first to last, and an attraction which will do the box office proud. There's never a false note about this grippingly imaginative story."
Picture Show wrote: "Thrilling spy drama, well produced and directed and splendidly acted. Eric Portman is again seen in the role of a Nazi, and it is a genuine tribute to his acting that this genial, charming man in real life, can give such a realistic portrayal of the Nazi Mr. Churchill visualises when he is pronouncing the word. ... Ann Dvorak gives a grand portrayal of the unfortunate nurse, and splendid support is given by Beatrice Varley, Martin Miller, Barry Jones, Henry Oscar, and Walter Fitzgerald."
Variety wrote: "A very workmanlike job on which time and money must have been lavishly expended, intelligently cast, directed and photographed, but, before going into general release, should in many scenes be cut to render them more comprehensive to the average cinemagoer. When this is done the picture should be a good feature for the general run of American theatres. The bestial character of the Nazi i ace, wearing a British uniform, Is admirably portrayed by Eric Portman, The outstanding characterization is that of a Swiss cook who is blackmailed into assisting the Nazi espionage in England. Temperamentally his technique is more that of an Italian, but he, nevertheless, gives an especially moving performance, His name, Martin Miller, is unknown, but report has it he is an Austrian refugee. He gives promise as a character actor. Second only to Miller is Beatrice Varley as his wife." Film historian Bertil Skogsberg in
Wings on the Screen: A Pictorial History of Air Movies (1987) called some sequences "fairly exciting but otherwise (an) uninteresting thriller." Aviation film historian James H. Farmer in
Celluloid Wings: The Impact of Movies on Aviation (1984) had a similar appraisal, that,
Squadron Leader X was "overlong". ==Preservation status==