The first Douglas military transport made its first flight on May 2, 1925 and completed Service trials at McCook Field, Dayton, Ohio, USA, by the end of that same month. Nine C-1s were ordered under the War Department Contract AC810 on the 1925 FY budget, having assigned the USAAS s/n
25-425 to 25-433 (c/n 158 to 166). They were followed by 17 C-1Cs, s/n
26-421 to 26-427 (c/n 366 to 372) and 27-203 to 27-212 (c/n 373 to 382), all being delivered by the end of 1927.