Il n'y a pas de fumée sans feu

I came across this during my walk along the coast near St Brieuc last week.At first I thought it was some kind of German blockhaus, but it wasn't made of concrete and it did have the same shape as they normally do. Plus, they aren't as common in the St Brieuc area as they are in Southern Brittany.

Closer inspection showed it was a "Four à boulets". I'm not really sure what this would be called in English, but it was essentially a big furnace used to heat up cannon balls to between 800° and 900° Celsius, so that they were flaming red when they rolled out the other side. It could take anywhere from 20 minutes to an hour and fifteen minutes to heat them up. Since most boats were wooden back then, the hope was that it would start a fire and cause the boat to sink. Assuming they actually hit managed to hit them that is, what with cannons not being the most precise type of artillery ever invented.

Wikipedia says these "ovens" were mainly used in the 18th and 19th century, and that some American ships, including the USS Constitution and the Merrimack, even had them installed on board. Though it also says that often just the quantity of smoke generated by them was enough to stop enemy ships from approaching the shore.

Ha - I wonder if this is where the phrase "Where there's smoke, there's fire" comes from?