The HyDRA started as an off-shoot of the IRIS. While iterating the IRIS design, I cannibalized some objects from it and got working on a unique idea. The idea is that HyDRA is a type of Forward Operation Base [or F.O.B. in military terms]. Its meant to be deployed, secretly, deep behind enemy lines.
What it does is carry a small wing of fighters, 3 to be exact, hence the name. Place-holder locations for the fighters can be seen in orange above.
Read more about how it was conceived here.
Then see how it progressed along with the attached fighters’ designs here.
Finally more progress on the Djinn Fighter, one of 3 fighters that can attach to the HyDRA here.