Best thing to do is to make yourself familiar with the 2016 DWP and IIP, you can download both PDF's at the link below:
Home : White Paper : Department of Defence
The relevant paragraph from the Integrated Investment Plan is:
Long-range electronic warfare support
1.20 From the early 2020s, Defence will acquire
up to five long-range electronic warfare support aircraft based on the Gulfstream G550 airframe with additional and modified systems. This capability will substantially enhance electronic warfare support to naval, air and land forces for operations in electromagnetic environments manipulated by hostile forces, with the operating cost, range and endurance benefits of a commercial airframe. The aircraft will be acquired in
two tranches and incrementally upgraded to maintain commonality with the United States-developed systems for long-term supportability and to maintain interoperability.