About April 20, 1918, German troops entered the Crimea and not meeting any resistance moved into Sebastopol. Almost simultaneously, from Constantinople came the German dreadnought Goeben, a cruiser, and four submarines. Along with them arrived the German transport General with several hundred German officers, noncommissioned officers, and bluejackets who were to board the Russian warships remaining in Sevastopol and to seize the staff and port establishments ashore. To take charge of all this force arrived Vice Admiral Hoffman who, it might be added, had served in the staff of the Russian Pacific Fleet during the Japanese War. Immediately the Germans commenced a thorough search on board all Russian ships and at all fleet shore establishments for secrets of naval warfare, especially any concerning mines, since the Germans knew the Russians had made great strides in this department of warfare. It was probable that the Germans had been informed, or at least suspected, that the British and French had to a large extent imparted their naval secrets to Russia, and now, with the collapse of the Russians, had come an easy opportunity to obtain them. As a matter of fact, the British Fleet had turned over to the Russian Admiralty several secret means of submarine warfare and details of net laying, given in such confidence that the Russians had been requested not to disclose them to naval attaches of friendly powers.
Considering the unexpected suddenness of the German advance upon the Crimea, it is not at all surprising that the activities of the German specialists and espionage agents in this quarter were highly fruitful. They searched all storehouses and workshops and scrutinized all plans found, seeking in particular a new idea in mines which the Russians had intended to use for blockading the Bosporus. The principle of this mine was that it maintained itself at a given depth without aid of either anchor or float, but exclusively by the energy of self-contained compressed air. The action of water pressure was utilized to regulate the cubical displacement of the mine. When the mine tended to lower itself, automatically by diaphragm action, its cubical content was increased, thus lessening its specific gravity. Then, when the mine tended to rise, its volume decreased and the resulting increase in specific gravity checked further rise. Any bubbles resulting from this action were unnoticeable on the surface even in a dead calm.
The first supply of such mines was manufactured just prior to the end of the war, and for this reason the Russians had not yet had time to use them. Further, it was definitely established that the Germans uncovered this invention and shipped all mines and pertinent equipment to Germany. After the departure of the Germans from Sevastopol no trace of the new mine was again seen in that port.
According to the plan of the inventor, Captain Kolbacev, such mines as these were to be strewn in the Bosporus and were to traverse this strait and the Golden Horn (the current here extends to both places) eventually reaching the Sea of Marmara. There the mines which had not yet accomplished their destructive purpose would automatically sink after a predetermined lapse of time, thus preserving their secret from the enemy. As a further development, these mines could be made to move back and forth along the Bosporus until they had been struck. This was easily accomplished because, as is well known, here there are two strong opposing currents, a surface current and an under current. The travel time of the mine was so calculated that having reached the end of the strait it would lower itself to the under current and, carried by this, return to the other end. Again, after a certain lapse of time, it would rise to the desired level in the surface current and repeat the journey. The length of time that a mine could thus travel depended upon the supply of compressed air contained in it to operate the mechanisms. This was usually enough for two weeks or more. One can imagine the result of sowing 30,000 such mines in the Bosporus and the Golden Horn, as had actually been proposed. Ships, bridges, docks, everything, would have been destroyed. No sort of obstacle would have been effective against this swarm of mines for ahead of them was to go a special advance guard of “clearing mines,” the same sort of mines, but having “whirlers” attached, something like propellers. Should one of these advance mines strike a net or other obstacle, naturally it would stop. The current would begin to turn the propeller. After a certain number of propeller revolutions the mine would automatically explode.
A second imposing mine device was the invention of another specialist well known in Russian naval circles, Captain of the First Grade Schneider. This was what is known as the “Schneider Bouquet.” The idea was cruel and cunning in its deception. To one and the same anchor, housing a clock mechanism, were attached five spherical mines. As soon as this “bouquet” reached the bottom one mine automatically lifted itself to a predetermined depth and threatened the enemy. If a mine sweeper removed it with its sweeping cable, the clock mechanism within the anchor began to function and after a desired interval, which insured that sweepers were clear, released another mine replacing the first at the same depth. Were this one removed or exploded, a third one rose, and so on.
The danger to shipping resulting from such a field is evident. Areas deemed to be swept clear are more dangerous than totally unswept waters. Who can say that the German Navy, having possession of this device, is not now using it as well as the compressed air mine against England? Perhaps this explains why in the present war several ships have met destruction in practically the same location.