Our greatest sailor, Nelson, always believed that strong, heavily armed forts could resist the attack of ships. When he was asked to reduce certain forts in Corsica by means of gun fire, he pointed out that stone walls were stronger than wooden walls, and that red-hot cannon balls from the guns of the forts might set his ships on fire. Since his day wooden walls have been replaced by armour plate, and red-hot shot by high-explosive shells. Nevertheless it is still true that shore batteries are more than a match for the heaviest armed battleships afloat. Of course, weak or badly-manned forts have been overcome by the guns of ships, as in the case of those at Alexandria, which were silenced by a British fleet in 1882; but as a rule ships run a great risk in attacking forts at close range, and are more than likely to come off second best. While a fort can only be put out of action by gun fire, a ship can be sunk not only by gun fire, but by mines or torpedoes. Forts can be strengthened to almost any extent, and protected by earthworks of all kinds, but there is a limit to the thickness and weight of the armour plate with which ships can be clad. Further, while shore batteries can be so hidden that they cannot be detected even from aeroplanes, a ship in action is in full sight of the fort, and is thus a good target. Then, again, hits made on the outer slopes of forts do but little damage. The only hits that really count are those which destroy or dismount guns, and such "direct hits" are few and far between. On the other hand, every shot that hits the ship is bound to tell, and the ship may be put out of action without a single gun being hit. You must also remember that while the fortress gunner is aiming at a wall twenty or thirty feet high and a hundred feet long, the ship's gunner can only fire at a low mound, or at a battery not more than four and a half feet in height. Even more difficult is the task of a ship's gunner when he is aiming at forts or batteries on high ground. It is not easy for a naval gun to bring an effective fire to bear on a target at a high level above the sea. Batteries on rising ground are difficult to reach, and when they are "spotted" they can be shifted to other positions, in which case the ship's gunners have to find the range all over again. When the shells from the ship's guns strike the ground they throw up columns of dust, and it is difficult for observers on board the ship or in the air to see exactly where the shells fall; but shells from the forts or land batteries drop into the sea, and throw up fountains of water which are clearly visible, and enable the observers on land to discover and set right all errors of range.