The LM RCS had a sort of backup whereby the hand controller could be switched to directly control the RCS jet solenoid valves, bypassing the RCS controller and the computer. Even in normal operation there was a "hardover" mode where the RHC's maximum deflection directly fired the appropriate RCS jets.

Not helpful in a power failure, granted, but the notion is still the same whether it's in a combat system or an experimental spacecraft. The capacity to degrade gracefully into somewhat less desirable but still operational mode is what reliability is made of.