EXTRACTS FROM SECOND ARMY HISTORY
SECOND ARMY SETS SAIL

CHOICE OF D DAY AND H HOUR

Factors limiting the time and date at which the assault could take place were numerous. The fullest co-operation between all three services was necessary to meet the individual requirements of sea, land and air without prejudice to the general intention or detriment of any one of the naval, military or air plans.

It had previously been decided that the assault would take place in daylight, and probably during the early part of the day chosen. This was agreeable to the Royal Navy which wanted the smaller landing craft without advanced navigational aids to operate within sight of each other. From the army viewpoint the advantages of protection by darkness were outweighed by the increased control afforded by a daylight operation not only of the assault on initial objectives, but of observed fire support and of the clearance of beach obstacles. The fly-in and drop of the airborne forces could still take place in darkness when the maximum confusion and surprise could be caused to the enemy.

Daylight was also more suitable for the air forces. The maximum use could be made of close support on pro-arranged and opportunity targets in the initial stage. With a daylight H hour it would also be easier to use a heavy bomber effort on the beach defences and strong points before they had time to oppose a seaborne landing.

The choice of the time of touchdown, and consequently of sailing from the UNITED KINGDOM was agreed between army and naval commanders. A landing at high tide was ruled out owing to the danger to assault craft from obstacles placed by the enemy on the beaches below high water level. It was desirous that these should be cleared by the engineers in the minimum depth of water.

A landing at extreme low tide, however, had also to be ruled out owing to a large outcrop of rocks on the LEFT sector. Sufficient time had to be allowed, either before or after low tide, to enable the passage of“ the landing craft over this natural obstruction.

A very delicate balance had therefore to be struck between the considerations of the natural and artificial obstacles, and the large rise and fall of the tide on the NORMANDY coast. Provision had to be made for the assault on any one of three days. After that tidal conditions were unsuitable for a fortnight.

On 23 May information became available showing the height of the rock outcrop to be about 3 ft 6 ins greater than had been thought. This necessitated retarding touch down time for the LEFT brigade of 3 Canadian Division by 30 mins on the first two alternative days of the assault, and by 35 mins on the third day.

To reduce the "stagger" between 50 (N) Division, 3 British Division and 3 Canadian Division, it was decided to make the time of touch down for the first two of these divisions ten minutes later on all three days. The times of assault were finally agreed upon between the three Services as shortly after low tide.

H hour was constant for all three Services notwithstanding the difference in times of touchdown. Detailed timings are shown in Appendix "D" and tidal to in Appendix "E".