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]

The Collaborative International Dictionary of English v.0.48:

Armor-plated \Ar"mor-plat`ed\, a.
   Covered with defensive plates of metal, as a ship of war;
   steel-clad.
   [1913 Webster]

         This day will be launched . . . the first armor-plated
         steam frigate in the possession of Great Britain.
   --Times (Dec. 29, 1860).
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

The Jargon File (version 4.4.7, 29 Dec 2003):

armor-plated
 n.

    Syn. for bulletproof.