So had this idea of a substance that could run between the layers of say armor on a tank. It would remain in a gelatinous state until exposed to oxygen and then immediately harden. So if a tank or armored vehicle were attacked, the holes would automatically fill in and become solid again. To keep the system ready, you could simply refill the glue/gel reservoir.
This same system could be used on aircraft wings to repair damage to wings and control surfaces. There could even be a laser matrix projected grid over the surface that the glue/gel would use as a guide for the repair.
Of course the implications for space would be great except for that whole oxygen catalyst thing. Maybe the stuff for space would trigger on lack of oxygen or cold?