"All measures designed to nullify or reduce the effectiveness of hostile air actions" defines which term?

The term "Air Defence" encompasses all measures aimed at neutralizing or diminishing the effectiveness of enemy air operations. This concept is critical in military strategy, as it involves a combination of active and passive measures to protect forces and assets from aerial threats. Air defence involves various tactics and technologies, including ground-based anti-aircraft systems, fighter interceptors, and electronic warfare techniques, all designed to create a multi-layered defense against potential aerial attacks.

In this context, "Control of the air" refers to the broader aspect of establishing superiority in the airspace, which can include offensive operations against enemy air forces and support to ground operations, but does not specifically focus on the defensive measures against enemy air actions.

"Point Defence" pertains to specific systems aimed at protecting a particular location or asset, typically against close-in threats rather than the comprehensive range of measures that "Air Defence" covers.

"Self Defence," while it denotes a general capability to protect oneself from an attack, does not specifically address the organized, strategic measures employed by military forces to counteract enemy air actions.

Overall, the definition provided aligns precisely with the comprehensive nature of air defence efforts within military operations, making it the most accurate choice.