Historical clue formulations

• Milieu for bathyspheres, with "the" — 2026-08-28
• Abysses — 2023-06-06
• Ocean areas — 2017-07-22
• Watery abysses — 2014-07-28
• Areas explored by submarines — 2012-02-20
• Ocean areas — 2010-11-07
• - — 2008-02-03
• Literary oceans — 2005-10-20
• Vast extents — 2001-10-06
• Vast extents — 2000-07-12
• Vast extents — 1999-10-16
• Oceans, to Longfellow — 1997-09-20
• Oceans — 1995-05-01
• Oceans, to Longfellow — 1994-05-24
• Ocean areas — 1993-12-02