Based on the dial design, logo design and crown design it is a model from the early fifties.
Those watch models did not have names at the time, the screw back cases were just marketed as waterproof.
The label « sei tacche » is a physical description which Italian collectors started using in more recent years. Some time ago I had discussions with an Italian collector who’s been collecting Longines since 2003 and he told me he was the one who had coined the word.
Edit/ add: if you ask a professional watchmaker to open it, you should write down the serial number of the movement, take pictures of the movement and the inside of the case back, and with those Longines can tell you the exact date it was sold to a distributor, and the country where it was sold.
With that you’ll know as much as can be known about your watch.
