In late 1929 and early 1930, due to armored vests and bulletproof glass for autos, the various big gangs around the country gave our police and law enforcement agencies a bad time.  Colt answered the problem with the Super.38 Auto on the good old model 1911 design.  The new arm shot a 130 grain bullet at 1300 feet and proved an answer to the problem.  J. Edgar Hoover's boys promptly adopted it for their side-arm.  It would penetrate bulletproof vests, armored car bodies if not too heavy, and bulletproof glass. The .38 S&W Special had been loaded with smokeless powder to equal the same velocity as it had achieved with black powder.  As MAJ Doug Wesson analyzed the problem, he soon came to the realization that the answer was to increase the powder in the .38 Special.  The answer was the .38/.44 S&W Special or the .38 High Velocity.  Smith & Wesson soon realized during testing that this round was too hot for their standard Military and Police .38 Specials.  A new model gun was needed to handle the increased pressure and recoil brought by the new round.   In December of 1929, the order to build 500 .38/.44 Militaries as they were originally called was issued by Harold Wesson.  The first orders were placed in early December 1929 which would indicate that the factory had announced the intent to manufacture them in late 1929.  The new .38/.44 Heavy Duty was identical in construction to S&W's earlier .44 Hand Ejector Third Model, with the exception of its .38 chambering.  Initially the gun was only offered with a 5" barrel, with a choice of blue or nickel finishes, weighing in at 40 ounces and checkered walnut service stocks.   In November 1931, Smith & Wesson began production of the .38/.44 Outdoorsman which was an adjustable sighted Heavy Duty.   On January 14, 1935 Harold Wesson ordered the factory to forge and machine 100 each 4" .38/.44 barrels.  There are recorded instances where 6.5 inch barreled Heavy Duties were manufactured.  There are also instances where the Heavy Duty was manufactured in .45 Colt caliber.  The 38/44 Heavy Duty was the most popular N framed gun in the 1930s with 11,111 manufactured before WWII halted production. The high speed .38 round in the .38/.44 led Doug Wesson, Winchester, and Phil Sharp to collaborate on a new, more powerful .38 caliber round they called the .357 S&W Magnum.  The new gun they built it around was a Hand Ejector with adjustable sights called the Registered Magnum. After WWII, S&W began shipping 38/44 Heavy Dutys in the summer of 1946.  These guns were Transition models which had pre war and post war characteristics.  These models continued until 1950 when the 38/44 Heavy Duty Model of 1950 was produced.  There were over 8,700 transition Heavy Dutys manufactured between 1946-1950.  The post war catalogs listed the Heavy Duty as available in 4, 5 and 6.5 inch barrel lengths, blue or nickel.  Production of the Heavy Duty continued until the early 1960s when they were called the Model 20.  The known Model 20s were shipped in 1963.  The last known Model marked guns, Model 20-2s were shipped in late 1964 to Austin Police Department.  In 1966, the Model 20 was dropped from the catalog.  During the period 1946-1966, there were 20,604 Heavy Dutys manufactured.  I have only one thing to say, " Make mine a Heavy Duty!" 

References: The History of Smith & Wesson, 1852-1945, Robert J. Neal and Roy G. Jinks 

Sixguns, Elmer Keith.