In Armor vs. Attitude, Ralph Kinney Bennett explains that “armor is a very relative thing” with this anecdote:
There’s a famous old story about some late 19th century Chinese warlord who bought some gunboats fitted with state-of-the-art Krupp armor. When he moved confidently up-river against a rival warlord’s forts, his opponent’s guns tore through the gunboats’ armor. He indignantly telegraphed a complaint to Krupp. The company wired back to inform him that his opponent had recently purchased the latest Krupp armor-piercing guns and ammunition. Tough luck.