4Greens
The Nuclear Attack Submarine(SNA) "L'Emeraude" was on location 9 days after the crash, and remained for another 30 days. From where-ever the sub came from takes time, and primary functions such as storing and crew changes etc.. need to be made before such a commitment can be made.
That's accepting that there may well have been other "lurkers" in the area earlier - such is the intrigue of international espionage.
mm43