The Aeromarine 40 was an American flying boat designed and built by the Aeromarine Plane and Motor Company in the 1920s. It was a larger and more advanced version of the earlier Aeromarine 39 flying boat.

The Aeromarine 40 was a single-engine biplane with a wooden hull and fabric-covered wings. It was designed to be used as a patrol and reconnaissance aircraft, and could be armed with machine guns and bombs for use against enemy ships and submarines.

The aircraft had a crew of three, with the pilot seated in an open cockpit in the forward section of the hull, and two gunners seated in open positions in the upper and lower wings. The Aeromarine 40 was powered by a variety of engines during its production run, including the Liberty L-12 and the Wright J-5.

The Aeromarine 40 was used by the U.S. Navy as a patrol aircraft in the 1920s and 1930s. It saw service in the Caribbean and in the Pacific and was used to patrol U.S. coastal waters as well. The aircraft was also sold to private customers and was used for various purposes such as pleasure flying, fishing, and transport.

The Aeromarine 40 was an important aircraft for its time, as it helped to establish Aeromarine as a major producer of flying boats and demonstrated the potential of these aircraft for military and civilian use.