Graf Spee's 11-inch shells were poorly matched to thin-skinned cruisers

Was Exeter merely lucky when Graf Spee's shells passed through without exploding?

Luck played a part, but the deeper issue was that 11-inch armor-piercing shells were badly matched to lightly armored cruisers.

Exeter's survival reflected a design mismatch in Graf Spee's armament. The 11-inch shell was slow-firing and required enough resistance to trigger its fuse, so thin cruiser structure could let rounds pass through before exploding. The weapon made more sense against Renown or Repulse than against the targets a commerce raider was most likely to meet.