Or if they cannibalized the sub and finally set off a working nuclear test fire from inside their Imperial Fortress? Such an initial test fire would bring the attention of just about any notable faction within range. This would also mean that the Enclave (and the BoS/NCR/anyone-else-we-feel-should-be-there will have to be tactical in their approach instead of just simply going into all-out war, because they won't be sure what kind of nuclear capabilities the Tinsui will have.

Thus, a powerful threat with plenty of unknowns, which allows lots of room for our characters' differing motivations.