Was it called that because it tipped up, not down? And why "high speed"?
In the collector community, it is called the fish hook hammer to differentiate it from the more common versions that came later. I say it looks more like a tomcat's tail than a fish hook but I didn't get naming rights.

Although S&W manufactured a short throw hammer before WWII for its K22 Masterpiece, they didn't call it the "high speed hammer" until after the war and primarily marketed it on the yellow boxes used for their K22, K32 and K38 target revolvers. It's actually printed on the box. S&W never referred to it as the fish hook hammer. That's "collector speak."
You will not find a model number on that gun because S&W didn't begin using them until 1957. It was simply called the Combat Masterpiece. It differs from the K38 Masterpiece target revolver by having a 4" vs. 6" barrel and ramp front sights vs. Patridge sights on the Masterpiece. It was designed to be holstered. AFAIK, the only service to officially use them was the Air Force. That doesn't mean that someone might have taken in over to VN as a personal weapon.
BIL brought back an M15 from Vietnam and he was in the Navy. There must have been some place over there that sold them them because he was a carrier wing aircraft mechanic and was only on the ground a few times.
There was a lot of wheeling and dealing over there during the war. I never drew a paycheck while I was there because there were a lot of suckers who thought they were poker players and happily donated theirs to me and others. When you lose all your cash, you start looking for valuables to cover your debt. Also, you could pretty much buy anything you wanted in the market or the ship's store for a fraction of what it could cost in the States. Most of us bought electronics and cameras, but guns were available. Also, you could buy a new gun directly from the manufacturer and have it mailed to you.