In 1915 Douglas joined the Connecticut Aircraft Company, participating in the designing of the Navy's first dirigible, the DN-1. In August 1915, Douglas left for the Glenn Martin Company where he was, at the age of 23, chief engineer, where he designed the Martin S seaplane. Shortly after Glenn Martin merged with Wright Company to form Wright-Martin, Douglas resigned to become, in November 1916, the chief civilian aeronautical engineer of the Aviation Section of the US Army Signal Corps. Soon thereafter he returned to the newly reformed Glenn L. Martin Company, in Cleveland, Ohio, again becoming their chief engineer. Douglas would design the Martin MB-1 bomber.