The caliber 28.5R-21 was introduced in 1953, and was Tissot's in-house automatic movement into the early 60s. The Seastar model was launched in 1954 as a water-resistant, three-hand steel sports watch in both manual and automatic flavors (and it remained this way through the 1960s) but you can find dressy examples as well. Here's a Seastar from 1958, in it's native habitat by the sea:
In the late 1960s and 70s, Tissot added the Seastar name to a range of sport chronographs as seen in this thread:
https://omegaforums.net/threads/vintage-tissot.63179/Click to expand...