Type IV Mine (DE)
The German Type IV Mine was adapted from their Type III mine for use by submarine minelayers, though it was also suitable for surreptitious use by vessels equipped with hidden vertical tubes. This article is based, initially, on a British report on German mines from July, 1917.[2]
| Type IV Mine | |
| Weight | – |
| Casing | 0.2 in. welded steel |
| Trigger | four impact horns |
| Charge | 220 lbs. T.N.T. |
| Primer | presumably tetryl |
| Detonator | 90 gr. fulminate of mercury |
| Buoyancy | – |
| Height | 41.75 in. |
| Diameter | 34 in. |
This was the type of mine discovered aboard UC 5.
The charge was of cast T.N.T. installed through a loading hole in the bottom of the cylindrical charge chamber. A intermediate primer of compressed T.N.T. was integral to the cast warhead and surrounded the primer proper.
Action of Laying and Detonation
German mines of Type I through V worked in the same manner. The mine and sinker went to the bottom together. After 10 or 20 minutes, a soluble plug dissolved to release the mine, which rose under its own buoyancy, trailing the tethering cable behind. When the hydrostatic depth gear in the mine determines that its proper depth has been attained, it fired to grip the mooring cable. After this, the depth gear and grip would be locked to prevent ratcheting upward with a rising tide. The British felt the depth gear was reliable and accurate.
When a contact horn was struck and bent, a glass tube of acid would break, and its contents would flow to a bichromate battery to energise it, causing the detonator to fire. This action was instantaneous.
Special Features
The British thought these were often laid with a time-release mechanism that would keep the mine on its sinker for several days after sowing, but none of those recovered by mid-1917 had any such mechanism installed. In light of that fact, they concluded that delayed unmoorings were perhaps unintended and attributable to mechanical quirks.
Footnotes
- ↑ German Navy: Part IV, Section 3. Torpedoes, Mines, Etc.. Plate 29.
- ↑ German Navy: Part IV, Section 3. Torpedoes, Mines, Etc.. pp. 18-26, Plates 28, 29, 34, 37.
Bibliography
- Admiralty (July, 1917). German Navy: Part IV, Section 3. Torpedoes, Mines, Etc. (C.B. 1182) The National Archives. ADM 186/228.
