CLARIFICATION: The rules aren't clear regarding when you remove "Safe to Land" or "Beachhead" markers. It only takes one hit to remove these - not the total minus the defense value (although for a beachhead - the terrain value is "0"). Thus if the Japanese player gets one hit on a US 2 defense strength controlled area that has a "Safe to Land" marker, the "Safe to Land" is removed. The Japanese player does not need to get 3 hits to do this.
The same principle applies to removal of Cave markers by U.S. Bombardments/Assaults. If any hits are scored, one Cave is removed - even if the terrain and/or Caves reduced the Damage Number to zero.
(I believe these are official - they were moved here from the More Information section, which was not the correct place for them.)
According the rules with errata on the MMP website:
"Beachhead or Safe to Land
markers are removed if the assault results in a Damage
Number > 0."
Damage = Hits - Terrain
So, I'm still confused.....