It is difficult to describe in small compass and non-technical language the various tactical formations employed in minesweeping operations. They were many and various. The Germans used their vessels in long lines, the ships being connected together by a light wire-sweep plentifully supplied with cutting devices, into which the mooring wire of the mine was expected to obligingly slip. This method suffered from the serious drawback that if any part of the sweep-wire caught on a submerged obstacle, such as a projection of rock, the whole line of ships became disorganised. There were also many other objections to this system, some of which will doubtless be apparent to the thoughtful reader. The formation usually adopted by British minesweepers was that shown in Fig. 28, in which it will be observed that each pair of ships is actually independent of the others, but is acting in company with them, and that the pathway swept by one pair is slightly overlapped by the following pair. In the event of an accident to one ship the next astern can immediately let go its own end of sweep-wire and go to the rescue of any survivors. It may be apropos to say here that the smaller class of minesweeper is usually blown to pieces if she touches a mine. [Illustration: FIG. 28.--Plan showing the usual formation adopted by British minesweeping vessels. _A._ Three pairs of sweepers. _B._ Sweep-wires. _C._ A mine entering the sweep of the second pair. _D._ A vessel following the sweepers for the purpose of sinking by gun-fire the mines cut up.] The set of the tide is another important factor which has to be taken into serious consideration when plotting a sweep. This complication enters into every operation, and its salient points will be made quite clear by referring to Fig. 29. The actual speed at which minesweeping operations are carried out depends greatly upon the engine-power of the sweepers themselves. In the case of trawlers and drifters it is seldom possible to drag the 300-600 feet of heavy wire through the water at a greater rate than 4 to 6 knots. M.L.'s can accomplish 8 knots with a lighter wire, while big fleet sweepers with engines of several thousand horse-power can clear the seas at 18-23 knots. [Illustration: FIG. 29.--Diagram illustrating the effect of tide on minesweeping operations. _A._ The vessels sweeping along the coast-line _B._ A fast ebb-tide is coming down the estuary _C._ Unless an allowance was made for this tide and mark-buoys or ships were placed along the dotted course _D_, the sweepers would unknowingly drift seawards along course _E_, leaving a space _F_ unswept and possibly dangerous to ships entering and leaving the estuary _C_.]