Most destructive of all weapons for underwater attack, however, is the mine, which sent to the bottom many a good ship during the Russo-Japanese war. The more deadly effects of the mine, as compared with the torpedo, are due to its heavy charge of high explosive, which sometimes reaches as high as 500 pounds. Contact, even with a mine, is not necessarily fatal; indeed the notable instances in which warships have gone to the bottom immediately upon striking a mine have been due to the fact that the mine exploded immediately under, or in close proximity to the ship's magazines, which, being set off by the shock, tore the ship apart and caused her to go down within a few minutes' time. This was what happened to our own battleship _Maine_ in Havana harbour, and to the Russian battleship _Petropavlovsk_ and the Japanese battleship _Hatsuse_ at Port Arthur. Enough has been said to prove that when the naval architect undertakes to build a hull that will be proof against the blow, not merely of one but of several of these terrific weapons, he has set himself a task that may well try his ingenuity to the utmost. Protection by heavy armour is out of the question. The weight would be prohibitive and, indeed, all the side armour that he can put upon the ship is needed at the water-line and above it, as a protection against the armour-piercing, high-explosive shells of the enemy. Heavy armour, then, being out of the question, he has to fall back upon the one method of defense left at his disposal,--minute subdivision into watertight compartments. Associated with this is the placing at the water-line of a heavy steel deck, known as the protective deck, which extends over the whole length and breadth of the hull and is made thoroughly watertight. [Illustration: Courtesy of Robinson's "Naval Construction" HOLD PLAN. INBOARD PROFILE. These drawings show the minute subdivision of a battleship. Below the protective deck (shown by heavy line) the hull contains 500 water-tight compartments. PLAN AND LONGITUDINAL SECTION OF THE BATTLESHIP CONNECTICUT]