Complex sentence: The main improvement over the A-variant is the dome installed over the main rotor, housing the AN/APG-78 Longbow millimeter-wave fire-control radar (FCR) target acquisition system and the Radar Frequency Interferometer (RFI).
Split into simpler sentences: The main improvement over the A-variant is the dome installed over the main rotor. This houses the AN/APG-78 Longbow millimeter-wave fire-control radar (FCR) target acquisition system and the Radar Frequency Interferometer (RFI).