The aircraft used in the opening scenes is a DC-3, but the aircraft seen taking off is a Boeing model.
As Holmes and Watson arrive in Washington, several continuity issues occur. The first is as they drive across Memorial Bridge towards the Lincoln Memorial. The footage shows them leaving the bridge, followed by a view towards the Memorial with them still on the bridge. They then pass by the Capitol before arriving at a hotel located at about 15th Street and Pennsylvania Avenue NW, an illogical route that would require a several mile detour to accomplish. Further, the supposed site of the hotel, judging from the back-projected footage of Pennsylvania Avenue, would be at the south side of the U.S. Treasury building.
Early in the film, a passenger aboard the train to Washington creates a diversion by blacking out the club car. The convenient panel he opens to throw the light switch does not exist. On standard single-level passenger cars in the U.S., such switches are in an electrical locker at the end of the car, only accessible with a punch key or skeleton key.
There is no Hotel Metropol in Washington, D.C., where Holmes and Watson stay in the film.
The copyright year in the opening credits differing from the release date in "Sherlock Holmes in Washington", with a copyright on the film of MCMXLII (1942), while the release date was April 30, 1943. In another entry, in the opening credits of "Sherlock Holmes and the Secret Weapon (1942)" the copyright year of the film I viewed showed MCMLXXIX which is 1979. The correct year of production/copyright and release would have been MCMXLII (1942).
Near the beginning of the movie, the bar/lounge compartment on the train was too wide to be on a real train car and the furnishings and passengers did not weave as the train was racing along.
The first plane shown is supposedly departing London for Lisbon. Yet there is a palm tree in the background. And the plane has "American Airlines" lettering, yet American had no international routes in that era.
The character Nancy Partridge is wrongly identified in the end credits as "Nancy Pattridge".
The Pennsylvania Railroad had no train named the Washington Express.
The train taking Pettibone and others from New York to Washington is powered by a GG-1 electric locomotive, but the sound effects and whistle are those of a steam locomotive.
The use of back-projection footage of Washington National Airport shows Holmes and Watson being welcomed and escorted to a car in a location that is actually the airfield itself. The real spot for arriving passengers is on the other side of the terminal building visible in the background. There was never a fence in the location suggested by the scene.
As Holmes and Watson are being driven to the airport at the end of the film, they are shown approaching the U.S. Capitol via Pennsylvania Ave. in the heart of Washington, DC. However, when the camera turns back to Holmes and Watson, they're passing a number of nondescript garages, junk yards and other small businesses instead of the large, official buildings located near the Capitol.
As Holmes are in the aircraft flying over New York, the pilot comments that they are now en route nonstop to Washington. However, the stock footage used here as Holmes looks out the front of the plane is an aerial shot looking northward toward the south end of Manhattan. Washington is of course south of New York City.