4 US Carriers in the Pacific
Enterprise
Yorktown (until April, 1941)
Saratoga (undergoing refit in Bremerton until April 1941)
Lexington?
In any event, at most 3 effective at any one time, and frequently 2 (Lexington was Pacific based but shifted around as needed for fleet exercises).
Langley by this point had lost its designation as a CV.
At this point the Langley is a seaplane tender. She was reclassified as such in the late 30s. Her designation is AV-3 now. I still look at her future sinking as the first American carrier loss though. Even though she was no longer CV-1.
On December 7, 1941: