Eval,
Those crashes came as a result of not being trained up and equipped to do the mission as you should recall and you are correct in noting how it so adversely effected the mission.
The key is appropriate and adequate training and equipment, and procedures designed for the area and threat as they are....not as they are imagined to be.
The Apaches presence will not stop a Chinook from being downed...RPG's fired from close range, small arms fire from close range, and large caliber machine guns and Manpads can always succeed. The key is the close in support the Apaches will be able to provide (should be able to provide) by directing direct fire onto the Bad Guys after the Chinook is downed and the crew/pax are engaged in a firefight with the Oppos.
You will find rockets to be more effective than the gun in all likelihood. The mindset that rockets are "area fire" weapons will have to change. Anyone talk to the US Apache guys and see how they altered their tactics after they got into action in Iraq and Afghanistan to see what they have learned? The Marines in their Cobras have gone to using run and gun tactics it appears.