From the foregoing it will be seen that the attack should be preceded and followed by a considerable period of darkness, and should more or less coincide {134} with the time of high tide. The latter only occurs about every twelve hours and takes place roughly fifty minutes later each day. The number of consecutive days on which high tide would occur in the middle portion of the night was, therefore, very limited. With regard to visibility, as far as naval operations are concerned, strong moonlight is almost as disadvantageous as daylight. Half the nights per month may be termed moonlight nights in that respect. The state of the moon on any particular night is known beforehand, the state of the clouds affecting moonlight may change from hour to hour. Just one more calculation. In mid-April the period sunset to sunrise is about eleven hours in length. Allowing two hours for the approach-passage through the danger zone, one and a half hours for the attack, and two hours for the retirement (to be completed half an hour before sunrise), it follows that the maximum number of after-sunset hours available for the open sea passage would amount to five. That was the best possible condition for us, but could only be utilised if high water occurred about four hours before sunrise. If high tide occurred any later our time of arrival would necessarily be later and our retirement could not be completed before daylight. If high tide occurred any earlier our time of arrival must be earlier, in which case there would be less dark hours available for our open sea passage on the way across. The length of the open sea passage would be approximately six hours. Thus even on the most favourable date, some of the open sea passage would have to be made in broad daylight. Six days before that (the tide being five hours earlier) the whole of the open sea {135} passage would have to be made in daylight, only the approach-passage, i.e., the last two hours of the whole trip, taking place after sunset. A rather complicated set of conditions, astronomical, tidal, and meteorological, was thus required. It was almost too much to expect that everything would be favourable during the possible period; it is practically certain that a commander who refused to move until all conditions were exactly as desired would never accomplish anything. Nevertheless we sincerely hoped that fortune would be kind to us. [Sidenote: Keenness of the Men]