The first hammer block was patented by S&W in 1914, and the prewar revolvers had the patent date stamped on the barrels-Dec 29 '14, but not all revolvers got them at the same time. 1917 Army's didn't get them until around 1919 or so, and some of the target guns didn't get them until the mid 1920's. The revolver that was dropped and killed the sailor during WWII did have a hammer block. but it was not functioning properly. The original hammer block was moved out of the blocking position by the hand, and returned to the blocking position by spring action, so if rust or grease jammed the hammer block, the gun would operate, but the hammer block wouldn't function. The current style hammer block operates in a positive manner in both directions, and will jam the gun if it gets rusted in place. I don't know about all the modern hammerless S&W revolvers, but my 940 doesn't have a hammer block, and the rbound slide doesn't have the actuating pin, nor does the sideplate have the milled recess for the hammer block.

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Tom
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