This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

Passage: During this period, the Weapons Station was the Atlantic Fleet's loadout base for all nuclear ballistic missile submarines. Two SSBN "Boomer" squadrons and a submarine tender were homeported at the Weapons Station, while one SSN attack squadron, Submarine Squadron 4, and a submarine tender were homeported at the Naval Base. At the 1996 closure of the station's Polaris Missile Facility Atlantic (POMFLANT), over 2,500 nuclear warheads and their UGM-27 Polaris, UGM-73 Poseidon, and UGM-96 Trident I delivery missiles (SLBM) were stored and maintained, guarded by a U.S. Marine Corps security force company.
What year was the Polaris Missile Facility Atlantic station opened?