More than twelve million dollars is to be spent in building great concrete forts and gun-pits on the islands and headlands, and arming them with batteries of twelve-inch mortars and fourteen-inch disappearing-guns. Most formidable of all will be the gigantic sixteen-inch gun, now at Sandy Hook, that can throw a shell, capable of sinking the stoutest dreadnaught, for more than twenty miles. Without these forts to keep them at a respectful distance, a few blockading vessels would have our fleet at their mercy as it came down the narrow channel in single column, or they might bombard the locks at Miraflores or Gatun. But modern battle-ships are too costly to be risked in a direct attack on coast-fortifications, which are usually captured by landing an army at some other point, and attacking the forts from the landward side, as at Port Arthur. For that reason, a permanent garrison is to be kept in the Canal Zone, of a brigade of infantry, a squadron of cavalry, and a battalion of field artillery, besides the gunners in the forts.
Every lock will be defended by earthworks against an attack overland. The operating machinery will be safely stowed inside the square center-pier (see diagram on page 182), beneath a thick concrete ceiling that should protect it from any bombs dropped from hostile aëroplanes. (It would be much easier for our soldiers to launch their own aëroplanes from a parade-ground or the broad top of a lock-wall, than for an attacking force to launch theirs from the deck of a ship.) The Gatun Dam is so thick and the lock-gates so many that there is very little danger of any one's blowing them all up and
