Historical clue formulations

• Depression shared by soldiers — 2016-04-22
• Detective's coat, informally — 2014-07-08
• Mariana ___ (world's deepest ocean point) — 2013-04-24
• You can dig it — 2009-01-20
• Channel — 2002-04-26
• Soldiers' ditch — 2000-10-10
• You can dig it — 1999-07-02
• Soldier's line of defense — 1994-12-27