Sponsored by the Post Office Department and bearing the company's designation DAM-1 (Douglas Air Mail One), the aircraft was virtually identical to the Liberty-powered O-2, but for military equipment and armament and having an entirely revised cockpit arrangement. Basically, it was a single-seater with an open cockpit located in the same position as the cockpit of the observer/gunner in the O-2. A fire-proof, aluminum-and-asbestos lined compartment with a capacity of 58.5 cu.ft (l.66 cu.m) was located forward of the cockpit and up to 1,000 lb (454 kg) of mail could be loaded into it through two hatches in the top of the fuselage.
As could be expected, since it was a direct derivative of the successful O-2, the DAM-1 (c/n 169) successfully passed its manufacturer's trials which began on July 6, 1925, in the hands of Eric Springer. Soon thereafter the aircraft was handed over to the Post Office Department under a one-year lease agreement. Operated primarily on the Chicago-Elko (Nevada) segment of the transcontinental air mail route, the DAM-1 was fitted with two 150,000 candle power landing lights under each lower wing tip and two 30,000 candle power parachute flares, and collective exhaust pipes extending well .aft along the fuselage sides were installed. Proving faster, having longer range, and being capable of lifting two and a half times as much mail as the old DH-4s, the aircraft gave complete satisfaction and its success led to the adoption in March 1926 of the Douglas M-3 as the new Post Office aircraft.
However, before expiry of the one-year lease, the DAM-1 was damaged in an accident and returned to Douglas. Rebuilt and brought up to M-2 standard, the original Douglas mailplane was redesignated M-1 and was delivered to Western Air Express in June 1926 to supplement its previously ordered fleet of M-2s.
Western Air Express's interest in the Douglas mailplane series began in October 1925 when this company was awarded Contract Air Mail Four (CAM 4), one of the first mail contracts issued by the Post Office Department pursuant to the 1925 Kelly Air Mail Act. To operate CAM 4 between Salt Lake City and Los Angeles via Las Vegas, in December 1925 Western Air Express (WAE) ordered an initial batch of five Douglas M-2s (c/n 244 to 248, registered C150, C151, C1489 to C1491). Still powered by 400 hp Liberty engines, the M-2s were fitted with a radiator installation similar to that used on the O-2BS and subsequent models in the |O-2 series and differed further from the original DAM-1 in having provision for two passenger seats and cockpit openings for the forward mail compartment and hatches.
On April 17, 1926, WAE began mail operations on the route when a Douglas M-2 flown by Charles James left Salt Lake City for Los Angeles while, later in the day, another M-2 piloted by Maury Graham flew the reverse leg. A little over a month later, on May 23, the first two passengers were flown between Salt Lake City and Los Angeles. By the end of 1926, in the M-2s, Western Air Express had carried 209 passengers, 71,414 lb (32,393 kg) of mail and 263 lb (119 kg) of express over Contract Air Mail route 4. WAE demonstrated its satisfaction by acquiring the modified M-1 prototype and ordering a sixth M-2 (c/n 252, C1512) which was delivered in 1927, and later acquired an M-4A).
In early 1926, the Post Office Department invited bids for a Libertypowered mailplane to replace the DH-4s on the transcontinental mail routes. Having already developed and demonstrated an aircraft meeting all the requirements of the Post Office, Douglas entered an improved version, the M-3. The M-3 had streamlined wires between the flying surfaces, instead of the cables used on the DAM-1 and M-2s, and other changes included improvements in engine accessories, instruments and night flying equipment. The long exhaust pipes added to the earlier Douglas mailplanes became standard while, for use by the Post Office Department, there was provision for only one passenger seat. Capable of carrying 1,000 lb (454 kg) of mail as opposed to only 400 lb (181 kg) for the similarly powered Air Mail DH-4 which it was intended to replace, the M-3 was selected by the Post Office in preference to the Boeing Model 40, and in March 1926 Douglas was awarded a contract for ten aircraft (c/n 255 to 264).
Within a year, the Post Office Department ordered an additional forty (c/n 303 to 342) which, designated M-4s, differed from the M-3s in having wings of larger area and overall increased span to enable them to lift a heavier load from the smaller airfields.
When the Douglas M-4s were ordered, however, the Post Office Department already planned to discontinue its own air mail operations and, as provided in the Air Mail Act of 1925 and Air Commerce Act of 1926, was progressively relinquishing its routes to commercial carriers. Finally, on August 31, 1927, by which time many of the M-4s were still in their delivery crates, the Post Office made a final mail flight between New York and Chicago. For a while indecision prevailed with regard to the disposition of aircraft no longer needed by the postal authorities and consideration was given to modifying sixteen of the Post Office's Douglas mailplanes for use by the Air Corps as 'cross-country airplanes'. However, the airlines needed them urgently and the Post Office fleet was put up for auction. Largest user of surplus M-3s and M-4s was National Air Transport (NAT) which acquired eighteen of these aircraft for use on the New York-Chicago route.
In addition to the forty M-4s ordered by the Post Office Department, Douglas built two modified aircraft. The M-4A (c/n 357, C1475) differed from the M-4 only in minor detail and was ordered by Western Air Express to bring its fleet of Douglas mailplanes to a total of nine (six M-2s, one M-1, one surplus M-4, and the M-4A). The final aircraft in the series, the M-4S (c/n 383, C7163), was ordered by National Air Transport and was a three-seater powered by a 410 hp Pratt & Whitney Wasp A nine-cylinder radial. For use in NAT's pilot training program, the aircraft was fitted with dual controls and instruments in the center cockpit.
Before obtaining the M-4S, NAT had fitted a Wasp A radial to one of the M-3s acquired from the Post Office Department while another of its M-3s was experimentally fitted with an enclosed pilot's cockpit. NAT operated its fleet of M-3s and M-4s until October 1930 while WAE disposed of its Douglas mailplanes shortly thereafter. One of these aircraft, the M-4 acquired by WAE from the Post Office, was later re-acquired by Western Airlines for display and publicity purposes. Restored once again, this aircraft was donated in 1977 to the NASM.
A further development was planned and construction of one aircraft designated M-5 and bearing the c/n 925-began. However, before completion, the project was terminated and the c/n and some of the parts already built were used on one of the O-2Ms built for the Mexican Government."
|
|
M-2 |
M-4 |
11/30/2006. Remarks by Jack McKillop: "This M-4 Mailplane was delivered to the US Post Office in 1926 and registered NC1475. It was used by the Post Office Department for their own airmail operations however, as provided by the Air Mail Act of 1925 and Air Commerce Act of 1926, air mail services were to be transferred from the Post Office to private operators.
One of the first private operators was Western Air Express (WAE) which was awarded one of the first mail contracts (CAM 4) from Vail Field, Los Angeles, California, USA, to Salt Lake City, Utah, USA, via Las Vegas, Nevada, USA. WAE made its first flight on this route in April 1926. This aircraft was sold to WAE in June 1927 and flew almost 914 hours carrying airmail before it crashed in January 1930. It was sold to several corporate and private owners until re-acquired by WAE in April 1940. It was registered as an M-2, NC150; this registration had been assigned to WAE's first M-2. WAE was renamed Western Airlines on April 17, 1941.
The first restoration of this aircraft occurred in 1946 but the it was not restored to flying condition and for the next 22-years, it remained in a Western Airlines hangar at Los Angeles International Airport. Starting in 1974, the aircraft and its Liberty engine were completely restored by volunteers and it made its first flight on June 2, 1976. After a transcontinental flight in May 1977, the aircraft was transferred to the NASM in Washington, presently it is on display at NASM's Steven F. Udvar-Hazy Center. It is believed to be the last Douglas mailpane in existence."