Having spent time served in USCG.air search,& rescue. Seeing a scope @2,000 feet is not possible,if there is no wake,due to same. My contention is perhaps from (stable platform) surface craft @ 1/2 visual range,air craft:less than 1,000ft.only if sub @ flank/full.(IMHO)

If there is any wind ocean is white with foam,(No wake) . .With MK52 gun fire control radar, periscope will not return a pip signal to indicate same. In 1961.