I had a RAID 5 (Linux software RAID) server which recently decided not to boot anymore. It seems to be a motherboard problem possibly due to not being protected by a UPS during a power failure. It managed to extend its slow death to the point of taking up plenty of my time without much reward but I know that the drives are fine. Is it possible to rebuild the RAID array even though the drives will have different numbers by plugging it into a machine over USB adapters? Is it possible any damage can be done to the array in the process by attempting to rebuild the array with the wrong drive numbers? I don't want to do a mdadm assemble --force unless I know it's safe. Is there something I can do to investigate if it will be safe to force the assembly? 
is it possible to recover a raid 5 array by using usb enclosures?
usb;data recovery;raid;storage;raid5
The short answer is: yes, it is possible.Linux software RAID writes some meta information on the devices such that you can easily plug them into another system (using another controller and so on) and use them there. Before doing any assembling, you can query the devices (status, look what Linux think what part of what RAID this device was etc.).When you are using USB adapters be aware that you can't query SMART information over it (or use other more sophisticated ATA commands).To be safe you should have a backup available. If you don't have a recent one you can copy the devices of your RAID5 via dd before issuing any mdadm commands.