What to tell Admiral Henderson in 1937

If Admiral Henderson received a lecture from the future in 1937, what should it tell him?

Prepare immediately with mass-produced escorts and submarines, and redirect the King George V armament program away from the 14-inch gun.

The proposed briefing warns Henderson that he has two years to prepare for war. Immediate orders would include about sixty Flower-class corvettes because they offer a rapid route to more escorts. The three U-class submarines historically ordered in 1937 would become roughly two dozen. A further recommendation replaces the King George V class's 14-inch armament with triple 15-inch mountings or another available heavy-gun programme. The 15-inch/45 option is favoured because it would also permit upgrades to existing battleships' 15-inch guns.