I apologize for my ignorance on the matter it's been a long time and Disk Utility has changed a bit since I had last done it. Don't feel like rooting around the internet. Trying to create a Tails boot drive.
An optional alternative that I use quite often is UNetbootin, works like a charm and despite it saying that the created USB cant be booted from a Mac, if done correctly the Mac is able to boot from the EFI file that is often stored in 'root of usb'/EFI/boot, for example Ubuntu 64bit has /EFI/boot/bootx64.efi on the root of the ISO that can be booted by your Mac.