When a newspaper mistakes gun calibre for barrel length

What is an especially bad naval fact quoted by a British newspaper since the Second World War?

He recalls a paper interpreting a 5-inch gun as five inches long instead of recognizing that the figure described the bore diameter.

The mistake confuses the diameter of the gun barrel with its overall length. It appeared in a national newspaper, possibly the Sun or Daily Star. The example is brief, but it exposes a recurring problem in public discussion of warships: specialist measurements are easy to misread when their conventions are not explained. This watch point helps readers decode the inch figures attached to naval guns elsewhere in the guide.