It's actually Longines calibre 989.
Then the whole tooling and calibre rights was sold to lemania and then incorporated into the house of Breguet.
Longines 989/990 = Lemania 8815= Breguet 591 minus the modern hairspring tech.
In fact a whole host of other watchmakers used this calibre in their watches e.g. VH in his Antiqua.
That is why vintage in house longines is still very much regarded and holds its value quite good. Much like the UG watches.
When Swatch group acquired all these brands, a whole marketing strategy and positioning was planned out for each individual brand. Sad to see that Longines losing its lustre and glory after the shuffle.
Breguet gets Lemania, Blancpain gets F.piguet, GO a clean slate and eta for the rest.