Which type of aircraft is an all-weather tactical electronic warfare variant based on the A-6 airframe?

The correct answer is the Prowler, which is an all-weather tactical electronic warfare variant derived from the A-6 airframe. The EA-6B Prowler was specifically designed for electronic countermeasures, including jamming enemy radar and communications, and providing support for electronic warfare in various combat situations. Its design builds upon the airframe characteristics of the A-6 Intruder, which allows it to operate effectively in multiple weather conditions while carrying specialized electronic warfare equipment.

The Prowler's significant capabilities in electronic warfare set it apart from other aircraft types in the options provided. In comparison, the Harrier, Phantom, and Hornet are designed for different primary functions, such as ground attack or multi-role combat, rather than specifically for electronic warfare missions.