The Collaborative International Dictionary of English v.0.48:

armor-clad \armor-clad\ armor-plated \armor-plated\
armour-plated \armour-plated\ armour-clad \armour-clad\adj.
   1. 1 protected with a covering of armor.

   Syn: steel-plated.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

armour-plated
    adj 1: covered with heavy steel; "armor-plated vehicles" [syn:
           armor-clad, armour-clad, armor-plated, armour-
           plated, steel-plated]

The Free On-line Dictionary of Computing (30 December 2018):

bulletproof
armour-plated

   Used of an algorithm or implementation considered extremely
   robust; lossage-resistant; capable of correctly recovering
   from any imaginable exception condition - a rare and valued
   quality.  Synonym armor-plated.

   [Jargon File]