For the arcade video game:
- Hey, It's That Sound!: Defender was Williams Electronics' first video game; they had previously produced only pinball machines. The sound effects in Defender came from the company's earlier pinball games, most notably Firepower.
- The NES adaptation of Defender II shares a few sounds with Punch-Out!!. Both games came out around the same time, so it's unsure who borrowed from who. The start-up tune of Defender II is the "begin round" music from Punch-Out, albeit with a Star Wars-esque flourish at the end. The tune that plays when you win a round in Defender II is the music that plays when you lose a match in Punch-Out. Lastly, and much more subtly, the sound of enemies exploding in Defender II is one of the sound effects that plays when an opponent in Punch-Out is knocked down.
For the pinball game:
- Hey, It's That Sound!: Defender uses the same sound effects from the arcade game — which, as noted above, were originally from Williams' pinball games, making this a form of Recursive Adaptation.
- Prop Recycling: The backbox for Defender are leftover inventory from Williams' shooter not-quite-a-pinball game Hyperball