Question:
Could you please give an example of example of how Coastal Defenses fire at commandos carrying out coastal raids?

Answer:
The commando arrives in the hex, the CD fires once against the NT/LC (you should move adjacent at night for maximum protection), and then you resolve the commando attack immediately when the commando “arrives” (not lands) in the hex.

So the commando, moving in the first naval move step (for example) faces one round of CD and then resolves the attack. It must still spend the 90 MPs to disembark, as do any other units arriving later (but during the same naval movement step) if they want to invade, and face CD if any still survives.

Source:
TEM 53