armor plate

a plate or plating of specially hardened steel used to cover warships, tanks, aircraft, fortifications, etc., to protect them from enemy fire.

Origin of armor plate

First recorded in 1860–65

ar·mor·plat·ed, adjective

Although on occasions they tried to use us as tanks, it was not successful, for our armor-plate was too light.

War in the Garden of Eden |Kermit Roosevelt
The naval officers and experts are all crying out against the folly of the Government engaging in the manufacture of armor-plate.

The Great Round World and What Is Going On In It, Vol. 1, No. 60, December 30, 1897 |Various
Another use of vanadium is in chrome-vanadium steels for armor-plate and automobiles.

The Economic Aspect of Geology |C. K. Leith
The Secretary did make the inquiries, and found that the actual cost of making a ton of armor-plate was $197.78.

The Great Round World and What Is Going On In It, Vol. 1, No. 42, August 26, 1897 |Various

Of course, the character of armor-plate has been vastly improved since that time.

Defenseless America |Hudson Maxim