At 11:27 , `` Yorktown '' was hit in the center of her flight deck by a single , semi-armor-piercing bomb which penetrated four decks before exploding , causing severe structural damage to an aviation storage room and killing or seriously wounding 66 men .
At 11:27 , `` Yorktown '' was hit in the center of her flight deck by a single 250 kg , semi-armor-piercing bomb which penetrated four decks before exploding , causing severe damage and killing or seriously wounding 66 men .