Raeder submits his response to Directive 16 in the form of a long memorandum outlining the difficulties inherent in an invasion - above all from the Royal Navy which he expected to be committed "fully and decisively" and might well cut off any forces that landed in the first wave.
The Naval War Staff delivered a detailed memorandum to the Supreme Command of Armed Forces in which it was stated that the task that would fall to the Navy was completely disproportionate to the Navy's actual strength - something that was not true of the tasks of the Army and Air Force.
The memorandum then explained in detail the difficulties in the operation:
1. The French ports from which the operation was to be mounted had been badly damaged by the recent fighting or were in other ways unsuitable;
2. The part of the Channel selected for the actual crossing presented great problems because of weather conditions, tides, and rough water;
3. The first wave of the invasion would have to be landed on the open English coast, and there were no suitable landing craft for such a landing;
4. The waters for the crossing could not be made or kept absolutely free of enemy mines; and
5. The vessels on which the troops and their supplies could not be even assembled in the embarkation points until absolute mastery of the air had been achieved.
But the most important part of the memorandum was the emphatic reminder that up until now the British had never thrown the full power of their fleet into combat. However, a German invasion of England would be a matter of life and death for the British, and they would unhesitatingly commit their naval forces, to the last ship and their last man, into an all-out fight for survival. Our Air Force alone could not be counted on to guard our transports from the British Fleet, because their operations would be dependent on the weather, if for no other reason. The Navy could support the movement by protecting the convoys to the maximum of its ability, and it could, in addition, lay protective minefields and make a diversionary attacks against the enemy. Any such minefields, however, would not offer absolute protection against such a desperate opponent and even if the first landing wave got across and ashore successfully, the enemy would still be in position to drive into the amphibious area and cut off the advance wave from reinforcements.
We in the Navy doubted that we could establish conditions that would guarantee even reasonably safe protection for a crossing of the Channel by the invasion forces. Circumstances were entirely different from those in the Norway campaign. There, surprise has been a most important factor in the operation, and even though complete surprise had not been attained, the magnitude of the operation and the wide spread of the movement among so many ports, all occupied simultaneously, had been beyond the power of the enemy to anticipate.
But in the case of England, no such surprise was possible. The major part of the transport vessels we possessed were craft designed for our inland waterways and were not even equal to limited voyages in the open sea. Many, in fact did not even have their own means of propulsion and had to be towed. To be ready in time, they would have to be assembled in the embarkation ports at the same time that the invasion troops were being assembled in the same localities. Such extensive movements could not be kept hidden from the enemy's air reconnaissance, not to speak of the very active intelligence agents he had throughout occupied territory. Hence this powerful and desperate opponent, lying just across the Channel and knowing that his very existence was at stake, would not only have advance notice of the invasion, but would be able with great accuracy to figure out just where such a landing had to take place and consequently to meet it with his entire defensive force.
It could not expected that even for a brief period our Air Force would make up for our lack of naval supremacy. Yet if this most important requisite could not be fulfilled nor all of the others, then the Navy faced an impossible task.