Rear Admiral Newton A. McCully, District Commander, Rochefort, France, and Commander, Sqaudron Five, Patrol Force, Atlantic Fleet, to Rear Admiral Henry B. Wilson, Commander, United States Patrol Squadrons Operating in European Waters
U. S. NAVAL FORCES OPERATING IN EUROPEAN WATERS,
FORCES IN FRANCE, DISTRICT OF ROCHEFORT,
U. S. S. NOKOMIS, Flagship.
19 March, 1918.
FROM : District Commander.
TO : Commander, U. S. Naval Forces in France.
SUBJECT: Employment of Submarine Chasers.
1. In view of the announced intention of the Navy Department to send one hundred and forty-four of the 110-foot 70-ton submarine chasers to European Waters, the following observations and suggestions are submitted.
2. First of all is the remarkable sea qualities of these vessels. Based on experience acquired in escorting ten of them across the Atlantic, during which there was frequently rough weather, and their behavior under such conditions, I consider that these vessels can live through any sea-- that they are more seaworthy than most larger vessels. They have a maximum speed of sixteen knots, a radius of 1200 to 1500 miles, and can carry safely a deck load of two tons in addition to stores, ammunition and provisions sufficient for their crews for three weeks. They are very lively, rolling nine to ten complete oscillations per minute, but are not more uncomfortable than destroyers. They are safe from torpedo attack on account of their light draft (seven feet loaded) and would be almost impossible to hit by a gun from a submarine, owing to their small size, quick maneuvering power and speed. It is believed that with no more battery than machine guns, three of them could force a submarine to dive.
3. Such qualities make these vessels formidable if properly handled. Their role is distinctly offensive – to sink submarines – and their weapon the depth charge. At present they are armed with two 6-pounder RF [Rapid-Fire guns] and four 50-pound depth charges. If the proposed plan of their employment should be adopted, one of the 6-pdrs. would be replaced by a machine gun, and each vessel would be fitted to carry ten 300-pound depth charges. Having equipped these vessels with an armament capable of making them formidable to submarines, the next part of the problem would be to find the submarine.
4. To send them alone or in groups to hunt submarines would be of little use. The submarine could see them probably more quickly than they could sight the sub, which could avoid them before they could assemble for the character of offensive action contemplated. The method proposed is, in addition to an escort, for the submarine chasers to accompany a convoy, not as escorts or for any defensive purpose, but solely for offensive action, the convoy under the circumstances constituting the lure which would tempt the submarine to expose itself, at which moment the chasers would get into action. This action has its guiding principle the concerted attack of three to six chasers, steaming at fifteen knots, in line across the probable location of the submarine after diving, distance between boats 100 feet, each boat dropping 300-pound depth charges at intervals of ten seconds, so covering a space of two hundred by eight hundred yards, within which, according to estimated effectiveness of the 300-pound depth charges, a submarine would inevitably be destroyed.
5. The difficulties to be encountered are due first to the low speed of the chasers. This is only sixteen knots maximum, and under conditions of construction can hardly be improved. However, it may be sufficient. Next is the tendency of the chasers to break down. With inexperienced crews this is a grave defect, but after three months’ experience, based on practice, this probability would be about one in ten, in a thousand mile run. For this reason as part of the unit should be a vessel capable of towing one or perhaps three of the chasers. This a patrol yacht can do.
The third difficulty is the maintenance of the chasers. For this there should be a tender, several of which it is understood are now under construction in the United States, and of which there should be one at least for every twenty-four chasers, with machine shop equipment capable of attending to chaser engine repairs, and with supplies for the crews. The tender would remain at the Chaser Operations Base.
A tank ship or barge carrying gasoline would have to be provided, as for a thousand-mile run twelve chasers would consume about 24,000 gallons of gasoline.
6. The plan of Operations would be as follows. On departure of a sea convoy, it would be accompanied by an escort of yachts for defensive purposes, each yacht being accompanied by three chasers solely for offensive purposes. It is not considered advisable that chasers should take any part whatever in the escort work – their mission will be to sink submarines, and all their efforts should be concentrated on that mission. The exact formation to be adopted while in convoy may easily be a subject of prolonged discussion – it is perhaps not a matter of first importance. The important thing is that the chasers shall have quick and accurate information of the sighting of a submarine. This will probably come from one of the escort, and might perhaps best be indicated by the firing of a gun, and noting the splash. At the same time a more definite idea may be given by signaling the location, referred to a squared chart with the convoy formation as Point of Departure. Such a squared chart should be feasible with a convoy of a large number of vessels, which can change its formation or course only after a considerable time. A suggested formation accompanies (Sketch #1).
7. On a submarine being sighted by a vessel of the escort or convoy, it will fire a shot, and as quickly as possible make the number by signal flags of the square where submarine was seen. All chasers making out the signal or locating the submarine proceed at full speed toward it, forming into line as they approach the spot, one hundred feet apart, and follow direction of submarine as nearly as possible, letting go all their depth charges at ten-second intervals when they think themselves over it. When depth charges are expended chasers may become part of the escort, and such chasers will then be of use in the rescue of crews if such work should be necessary. Each chaser can carry ondeck comfortable and safely one hundred men.
8. In these tactics many minor points will be noted in practice. Although the chasers may adopt almost any suitable formation during the day, yet at night or in thick weather precautions must be taken so that they will not be fired on by their own vessels, as when seen indistinctly they very much resemble submarines themselves. This would require that in such weather conditions chasers will remain in groups of three. Sighting one of them, with such a rule, would not be probable without sighting at least one other, and it will not be likely that any such group of vessels would be mistaken for an enemy. In case of a chaser breaking down it would be taken in tow by its section leader (yacht) and preferably take station astern of convoy. In case of a chaser breaking down at night or by error getting out of position it would turn on its running lights. In order to make them less conspicuous the masts of chasers should be cut down to top of pilot house.
With present lack of destroyers such employment of submarine chasers would have peculiar value.
/s/ N. A. MC CULLY.