From Conflict of Nations Wiki
The helicopter gunship will be a viable enemy to infantry and lightly armoured targets. Allowing you to land on friendly carrier decks whilst flying under the radar of SAM and TDS makes them flexible in their strategic potential.
Attack helicopters are particularly useful on the offensive against hard or heavily armoured targets. Very similar to the gunship, they have NOE, which allows them to fly under radar detection of SAM and TDS.
The anti-submarine helicopter specialises in detection and engagement of submarines and surface vessels, with torpedos and missiles. The features available on other helicopters carry on here, able to detect submarines, use carriers and fly under the radar from SAM and TDS.