Inbetween conflicts the U.S Military would disband the Sniper program and upto and including Vietnam and would have to bring out this old book to brush up on where to start at bringing them back out . Since Vietnam thoes that operate in this fields have made sure to keep it going.
That tradition of raising marksmen and then disbanding them starts with the American Revolution itself. The first unit raised by Congress, The First Pennsylvania, was composed of riflemen. They served only one year and then were disbanded when their term of service expired. Washington then asked Daniel Morgan to raise an ad-hoc 500 strong rifle regiment. They earned fame at Saratoga and afterward a couple of companies were dispatched to the Wyoming Valley to fight marauding Indians. Then they too were disbanded. Washington then raised another ad-hoc unit of riflemen under Maj. Parr, but they stayed in NY and didn't fight at Yorktown.
After the Revolution was won, there were no rifle units until the First Regiment of Rifles was raised in time for the War of 1812. The unit that fought at Tippecanoe weren't even armed with rifles (shortage of 1803 Rifles). During the war, over three more rifle regiments were raised, but only the first survived the post-war cut and then they too were disbanded.
There was a brief period of mounted rifles, but they were converted to cavalry. During the Civil War, many civilian/volunteer rifle units were taken into Federal Service. The most famous was Berdan's First and Second United States Sharp Shooters. Despite their feats, both were disbanded before the Civil War ended (depletion in #s and three years term of service expired). Post-war, while sharpshooters proved their value, they were not seen as necessary for the frontier army that the US Army reverted to. The fast moving fights on the plains were seen unfavorable to having them.
There were no sharpshooter units that fought in the Spanish American War, but known marksmen were called for to take out the Spanish sharpshooters who were sniping stretcher bearers. During WW I and WW II and Korea, the US was caught unprepared for sniping. Our first WW I sniping manuals were based on British ones.
Today the sniper has a permanent place in our armed forces' TOE. They are a force multiplier.
The above was my drawn from my book on the subject.