Bush and Hornblower refer to the shell which Hornblower extinguished as a "five inch". The cannon was clearly no more than a 12 pound gun which would have had a bore diameter of about 3.7 inches. A five inch gun would have been too large to be easily moved by hand as shown in the scene.
After the long boat is destroyed the French are shown loading
a shell into a field piece. It makes a rolling sound as it goes down the barrel. This would be inaccurate. A shell fit tightly enough to require ramming, and a shell would have been carefully positioned in the barrel so the fuse would face away from the powder charge.
When Jerome Bonaparte introduces himself he presents as Jerome Lucien Bonaparte. Lucien was his other brother. His name was Jerome Bonaparte, born as Girolamo Buonaparte.
The sailing master calls out, "clew up the mainsail." There is no mainsail on a square rigged ship. The lowest sail on a mast, which is the largest, is called a "course." Each mast would have a course. The fore course, main course, and mizzen course. The sails just above the courses are the topsails. Larger ships would have both an upper top and a lower top. Each sail is prefaced with the mast it is on. From forward to stern are the fore mast, main mast, and mizzen mast.
The snow is clearly fake. There is no drifting, despite the wind blowing it sideways; the deck is perfectly evenly covered, with no footprints; and there is no sign of any snow on the row boats, or the shore. The trees are all green and the land shows no sign of winter.
During the final confrontation, Doughty is saved by Styles and Matthews from a cannon that smashes through the gratings. As the it finally falls, it bounces unnaturally, without leaving a single dent in the wooden deck, as it would happen with a real cannon. Actually, one of the sides breaks off, very briefly showing a yellow, foam like material underneath, revealing the cannon is a lightweight prop.
After the discovery of the canons in the barn, Hornblower and his companion are walking in a field with a period cottage on his right. Attached to the chimney is a TV aerial.
About 55 minutes in, a French horseman is seen riding towards a cottage - the cottage has a very visible and tall TV aerial.
After the wedding the hand drawn coach has modern electrical bulbs.