A submarine mine of to-day consists of a mine case, shaped like a ball or egg, about one yard in diameter, mounted on an anchor in the form of an iron box about 30 inches square, connected by a wire rope mooring cable, about ⅜ inch in diameter. The mine case contains the charge of high explosive—300 pounds of TNT in our mines—and the firing mechanism. The combination stands about 5 feet high and weighs 1400 pounds. Four small car wheels on the anchor run on steel tracks, allowing the mines to be easily moved along the decks to the launching point.
The Sequence of Operations After a Mine is Launched.
When the mine dives overboard, the mine and anchor come to the surface and float for a time, still held together, part of the mine case above water. Outside the anchor is a 90-pound plummet, containing a reel of ⅛-inch diameter steel wire “plummet cord,” made the same length that the mine is to be below the surface. Thus, if the mine is to be 160 feet beneath the surface, the cord is made 160 feet long. The plummet drops off when the mine goes overboard, unreels its cord, coming to the end with a jerk that trips the slip hook which holds the mine and anchor together. The pull on the cord also lifts the latch on the reel inside the anchor, allowing the mooring wire to unwind. The nearly solid plummet tends to sink faster than the more bulky anchor, thus keeping the cord taut until the plummet strikes bottom. The cord then at once slackens, releasing the latch, locking the reel, and preventing any more mooring wire unwinding. The anchor, continuing to sink, pulls the mine under until the anchor strikes bottom. The mine is thus finally moored always at the desired depth beneath the surface, no matter how irregular the ocean bed may be. The mine cases are buoyant enough to pull straight up from their anchors ordinarily, but in a current they are swayed away from the vertical, which dips them down somewhat deeper than intended. For this reason, any locality where the currents are strong is unfavorable for a minefield—one of the difficulties the British Navy had to contend with in closing the Dover Strait.
The new mine having, by October, been carried past the experimental stage as to its principal features, by the Naval Torpedo Station at Newport, R.I., some important mechanical details of the mine yet remaining were now worked out by the Baltimore, Captain A. W. Marshall, working directly under the Bureau of Ordnance. By the time complete units were ready, the Baltimore had been sent abroad, so the proof testing devolved upon the San Francisco, Captain H. V. Butler. This came in March and April.
No throw of the dice was ever watched more intently than those first proof tests. Upwards of forty million dollars had been staked on them and were already half spent. Results on the first day made us feel easy, but it was two days more—from various delays—before we succeeded in exploding a full loaded mine. This had been planted in Chesapeake Bay, well marked and guarded, in the very same deep hole where a whirlpool effect troubled the German submarine Deutschland on her first return trip. It was not possible to place the mine far from the fairway, however, since the water elsewhere was not deep enough for our purpose. Early the second morning, the battleship Arizona came along, heading too near it. The signal “You are standing into a minefield!” sent her rudder hard over and engines full speed astern. We could see the mud stirred up, from two miles away. Since we could not get the mine up, what a relief it was when it was set off at last by sweeping!
The final proving of the mine as a whole, which was completed in April, off Cape Ann, did not take place until after several cargoes of mine parts had been shipped abroad, but the mine’s success, from its first trials, showed how careful and observant had been all those who were concerned in its designing and testing.
The prospect in October was that the shipment of mines would begin in January, but through delay in completing the detailed plans and from the abnormal industrial conditions prevailing, these shipments did not attain a regular flow until May, so that the ships and the mines were ready together.
Secrecy, as well as timely delivery, caused the manufacturing to be partitioned among 500 contractors and sub-contractors, some of them as far west as the Mississippi. Certain mine parts from different makers were put together by still others, and all parts flowed toward Norfolk, Virginia, the trans-Atlantic shipping point. Planning this dividing up, placing the contracts, and arranging for the inspection of all—taking into account the transportation involved and the many different kinds of firms—wire rope makers, automobile concerns, foundries, machine shops, electricians, die-presses, and even candymakers—it was indeed a complex web. What tireless industry and what endless patience under pressure went into this work, only Commander Fullinwider and his assistants can fully appreciate.