In the 1950's, Beretta found itself hustling for sales "in the middle." Though the 1934 was still being used by the Army, and the Italian Navy had adopted the 1951 9 mm, the sales of the 7.65 x 17 mm, M1935 were diminishing. Increasingly, they found themselves also rans, especially outside of Italy. Something had to be done before they found themselves completely out of the picture. Tulio Marengoni and the boys set to work and by 1957 had a completed design in production, ready for sale in 1958. They were an evolution of the earlier 1935 pistol, retaining the open slide and the resulting excellent reliability and accuracy, but correcting the miserable safety and having a sleek, modern look. For my money, the M70 shares with the Mauser HSc the bragging rights for all-time best looking semi-auto pistol.
The early Model 70 had the funky push button safety found on the Model 1951 9mm (How Mack Bolan ever came to regard such a travesty as "La belle Beretta" is an oddity known only to the author. No one who used them would ever describe them as such.) A cross bolt safety at the top of the rear of the grip served to render the gun operable or not, depending which way the button was pressed. This did not serve to ingratiate the pistol with the American gun buying public. After about 4 years, the safety was redesigned to more conventional, 1911 style thumb safety, which was retained through the balance to the production life. The name was slightly altered, so that the 70 became a 70S allegedly in 1977, reflecting the safety change. The 70 series Berettas continued in production until 1985, but they had been increasingly supplanted by the "80" series of DA/SA pistols.
There seems to be plenty of misinformation on the web concerning these pistols. Mine has an "AI", stamped on the frame, not the barrel. None that I have observed have magazine safeties--the "S" reflects the thumb safety, not a magazine safety, at least IME. Mine is ~6 1/2" long, not 6.875". It weighed 23 ounces on the nose, not 23.8. Mine is a 380 ACP, but others were chambered for both the 32 ACP as well as the 22 LR. The Israeli Mossad issued the 22 pistols back in the 70's for both sky marshal and assassination use. Mine is the relatively rare, two-tone, nickeled slide with a blued frame. I have read that some were available with an aluminum alloy frame, mostly 22's, but some 32's as well.
As far as shooting goes, mine is excellent. Though the Silver on silver sight picture left a lot to be desired, I had no trouble shooting a 2 3/4 inch group at 15 yards from the rest. And at 25 yards, I could cover 7 of the 8 shots with the palm of my hand, weaver style, off-hand. I would take one of these for a CCW ahead of a lot of guns.